Let's start with FTL jamming, as it easiest problem here and somewhat defines the course of actions as well.
There is a typical trope - the gravity of a star interferes or denies the lock for warps etc.
in which way it does that's quite flexible, meaning how strong it affects things and which ways there are to overcome the problem. And as an example, it may affect the precision of jumps with a certain probability, so u miss half of the system if u try to land here and appear in some random place. This parameter may be adjusted as the perfection of technology of the jumps, so as to have some fundamental limitations of the size of warp jump bubble vs energy spend on the jump - so it may easily leave some place for ships on a smaller side with a humongous reactor - basically flying reactor type vessels - to be able to land closer and be able to penetrate in the system - recon, black ops, and other infiltration.
So it may be not that bad, and may even have some roots in reality. unfortunately for the scenario, even if there is some flexibility on the ship side, it lacks flexibility on the volume side, even if it may lead to interesting scenarios in some binary system, interesting story-wise - main hero, smart brains, smart plans, etc.
The artificial jamming system indeed allows more flexibility, and coupled with detection makes sense, even if it does not deny potential natural resistance of bent space-time close to a star, which can take some load from those artificial means - making them small enough, making them consume less energy - like they do not necessarily create the jamming force, but artificially manipulate existing one to amplify it, and work when it really needs to work based on the detection. Also may have the same requirements to overpower them - small ships with toons of energy, with difficulty, and a bang if it persists and fails p that nuances up to your story.
in terms of the area of effect from individual suppressors - it does not have to be big, as it like mobile phone towers, coverage is defined by how much and where place them. And in that sense, one covering 10-20 light seconds may be good enough.
Fortification aspect of that is quite flexible, especially with artificial means, and I would say that 60a.u. radius creates a sufficient size battlefield for different defense strategies so as for offensive actions with the weapon u choose. And if one needs and places more importance on things, spending resources by placing those suppressor beacons further, and spending more resources that buffer zone can be grown bigger. it isn't impenetrable as u warp 10-20 seconds from the border and may start to penetrate it in usual space, not necessary with big ships, but some special ops means, or by some overpowered small ship try to land deeper and create beachhead if lucky. plenty of flexibility there.
But it needs to keep in mind that the main fortification of a star system is that - offender has to bring all the means of attack, and attach himself to star system resources, while defenders do not have to move anything and are in control of energy and materials(at the start). The advantage of an attacker is that they select the time place and the way of attack, while defenders have to expect it from any side and react and hope they guessed the plans of the attacker. So defenders have to spend more resources on preparing, and if they do not fail that - they can have an overpowering advantage in firepower if they are given time to move those things to places where they need to be. Meaning that even without any jamming effects, they have ways to make jumping in the system to be a wrong move by "stationary"-nonftl guns whatever floating in space. They have all means to do so - as star systems are the only sources of resources - as matter, and in some sense, as the energy goes, and they do not have the problem of FTL transport it, it all already here and just needs to be shaped and placed beforehand.
defensive aspects for chosen weapons.
as a side note, your selected set of weapons ready calls for humongous battle scales, on the levels of K2 civilizations, billions upon billions cap ships, and I can't recall, and do not know anyone who successfully fared the territory, or was close to it. By K2, I do not necessarily mean technology-wise, but resource availability and readiness to use those resources - the whole star system is ready to provide to them. I guess u aren't going in that direction either, maybe for the better as typical Nicole Dyson beam thing such utter nonsense, in some sense - lacks the flexibility, not as good as some imagine it to be, lacks energy density and all that. But it needs to keep in mind that any spacefaring civilization without a good percentage of use of a star system they are in - is weak and lacks the capacities, including ones to defend themselves, and overall it is something wrong with them.
UREBs aren't bad
- Magnet drones seem to be a viable way to help deflect these, granted they're significantly out ahead of you
it is good u know that move, and placing them a million km away can be sufficient, we have enough space for that. As u know even supernovae blast isn't that bad if u far enough from it.
it more likely them being good at fry electronics, at least over time, over a large area, so beaming them in a narrow beam maybe not the best way to use them it more like your long projected, fast delivery ECM means - to blind the attacker, create plasma bubble around it in millions of km, smokescreen your actions. So as a jammer for signal transmission, electronics disruptor. But if u can focus fire it then it may be useful as well in some cases.
Laser Coupled Particle Beams - this one is better suited for what u envisioned for UREBs, that's a nasty sht - it is harder to deflect, if not prepared for it, it will place its energy in the target more effectively. But in some sense it easier to defend from it as it will be more effective to dissipate in some remote shield - gas cloud as an example - so its strength may be its weakness. But spending mass for protection will limit the attacker, so time for a sweet shot will come.
So depending on the situation, free u fantasy - even if those two(UREBs, LCPBs) aren't ultimate weapons(nothing is actually) - u may alternate between them depending on the course of the battle, opponent's actions, and your capacities. it is a middle, long-range weaponry - one which exhausts ships delta-v.
Lasers - overrated, by a lot, especially as ship weapons. However, for capital defense systems can be a thing as fastest of them all, and as capital means not necessarily need to worry about efficiencies being connected to star as their energy source, and can deliver constant debuff over a large area so maneuvers are futile - doing constant overheating damage narrowing the window of opportunity for an attacker, as time goes, and be one of the main specialties of defense capabilities of a star system. Be somewhat one of the cores for energy-hungry weaponry, placed somewhat in the inner of the star system. So as one of the well-protected means to deliver energy for more distant installations in peaceful time so as in wartime.
remember star is the biggest energy source to be used in war activities, the opponent can't bring one, but u have it. (this matra holds quite long and far in tech tree). So it is a long-range, over a large area, capital defensive weapon, not suitable for mobile fleets.
Macrons - not bad, but not great. Mostly close combat thing 1-2-3 light second distances. what it can be good at is antimissile defense/means. if the setup which fires it is big, then u have dedicated ships for it to be your missile shields, covering a group, or more likely forming a barrier in front of something, in front of some direction, in direction of groups of ships, or as part of extended planetary defense, space habs defense.
Missiles and drones of various sorts. - yes yes, more of those, flood the space with the stuff. All sizes, all purposes.
The system has years to prepare and establish the defense system, your star shines and wastes a lot of energy if u do not use it, your gas giants are starving to become something else and be reborn as space ships and missiles and their fuel and serve their masters.
So as u may satisfy their desires and build many many missiles and drones, which due to the magic of kinetic energy is one, is the same.
Those things do not have to be hidden, and they can serve the dual purpose of navigation, monitoring, communication, science, rescue, transporting stuff, etc. So u may be in constant communication with them, and they can be in constant periodic communications between themselves, periodically physically checks they arrive for, etc - to make sure u still have control over them and no hacking shall pass. But most of the time war functions are dormant.
- remember that any scientific, civilian equipment on a drone means more bang for it as kinetic missile projectile. So load it with more side functions it does not matter and does not affect its functions.
- your FTL suppressors also live in the category, and that's why it does not matter that much how big of a suppressing bubble do they create, just make them more. 10-20 seconds is good enough if they are small enough.
- those things are your first response and source of misunderstanding by blowing up some innocent lone alien ships, who was trespassing, who was not aware of things. They are the countermeasures for black ops ships, piracy, and overall making sure that freedom is free, so as when the time of invasion goes on they more and more become a means to wipe the enemy fleet as they accelerate in its direction. Takes hours and maybe days to accelerate and arrive in big numbers(as they are semi evenly distributed across the system) but more time it takes a bigger hammer they become, more and more of them arrive from a bigger volume. And they are true might of defending side, defenders just need to drag the situation, stall for time and manage to target those and land them on the enemy.
infiltration, hacking, other means to compromise defender's control over defending means.
Creation of beachhead, and fight for control over some resources to stick to and develop them in a lever for a fight for control over other resources.
- if your insurgents manage to infiltrate to those inner system laser defense setup, partial control as an example then they can support your invasion for some time, an hour or 5-10 hours, opening an opportunity for an attacker to take roots at Neptune or maybe even Jupiter. By timely disrupting power supply, or not letting it drain when it's a second phase.
A big celestial body is a good resource as it is one of the biggest shields u may get and which puts Nicole Dyson beam to shame. So as it may be a source of materials, despite 9x percent of it being hydrogen-helium, it has other stuff in it, so as it is a thermonuclear fuel station. And if u not in magical energy source territory then it also adds value.
So celestial bodies are the ability to increase your invasion forces, be released from concerns of limited mass they are capable to throw around(as shields as propulsion, etc) as time goes, so as an ultimate half shield. But most importantly it is the source of materials u build your own missiles, drones, ships to replenish your supply. And if attackers are successful at latching on it, then it may become a big problem over time. And infiltration to prepare that opportunity, maybe build up some forces there already - may be essential to overall success chances.
Defender's mission is to disallow that to happen and ripoff the leach if it happened and clean de-attach attacker forces from the ground, cut the potential resupply route, and then grind it off the system.
So focus less on tactical aspects of battles, they really up to u and your system, if u keep some ground-laying aspects of them. Tactics are less fundamental and prone to change significantly dues small changes in advantages disadvantages of weapons and other aspects of systems used. it's a typical shield and sword situation - it has no beginning so has it no end.
So in the first place identify their strategic goals, what is important for those guys. And where is the need will be the means, and all that can develop and be a thing to change over time. So goes it about defense, so as about attacking.
First of all, u have to determine a unit of that combat, the meaning of what is it a unit, what it consists of.
imagine it to be one single ship, is not necessarily useful, as there are clear problems - as u mention there are big weapons, and so if u need that weapon to be battle capable u need a ship for it alone, but the ship will not have battle round capacities, so u need more specialized ships.
if weapons are small enough to be placed in one ship, then it can be one ship, but if it leads to the reduction of capacities of that type of weapon it makes sense to have dedicated ships, instead of one.
So we may mean a fleet, but in sense of today's air-carrier fleet - a set of ships which has dedicated roles to conduct specific tasks - in our space case like a general battle, penetrative invasion, black ops, hacking, etc. Like a system of parts from which an actual mechanism, a space sword is made of. So one ship mano a mano is not necessarily a thing, as loss of few ships is a rounding error, and a hundred ships maybe not appropriate to call a fleet in a big sense, as it may be just a drop in billions upon billions of invasion forces. That needs to keep in mind. The smallest unit of battle can be a composite thing, made out of different ships.
But at the same time, it does not necessarily mean proportionate crews. one guy per such unit or one suicidal Ai can be sufficient. So if we take as an example typical depictions of ship roles - one may have the same set of roles - captain, gunner, mechanics - and the crew of those small ships is the crew to the whole set of ships in our case.
I like The expanse, overall, as there are things I hate, but they got certain things right, and definitely better than many before them. But that amplification of humans power by means of groups of separate units, with way limited Ai on the level of stupid mobs from starcraft, is definitely not there, not even talking about what we can do today and space is a much simpler environment for them to exist so there is no way not to use them.
Jamming of communications may make sense against such units, to prevent timely and complex group strategies but won't affect that much basic strategies if not a lucky hit, so they are loosely stuck together 1-20 light seconds - as being too compact also has its downsides. with some drones, which are on the smaller side as glue for different goals.
if we think about classical one-to-one ship combat then The expanse got the moment right - missiles, counter missiles. what they need more of, probably is different warheads, but on the other hand with close combat does not matter that much.
So all that is more than small fleets u talk about, but it is a small fleet by its form, not the role - the role is like a single ship.
Small fleet is a group of those smaller fleets which act on thousands of it and on the scale of a.u.'s
This way they can reduce the efficiency of those passive drone sleepers network which defenders may have - by eliminating them over large are, intercepting them far from the target before they got to speed gaining efficiency, increasing the time defender has to spend to bring those means from further away. it isn't an absolute strategy, but it definitely is capable to reduce the efficiency of defender means over a longer period of time.
While the whole attacker force maybe billions of those small fleets and u have to imagine it being a swarm of ships against a swarm of defense. And it has a place for tricking opponents, tricking automatic algorithms and simpler Ai's - exploiting their intellectual weaknesses. Distraction, the disguise of actions and intents the whole set of typical things.
So as u can start the action from outside the system, wait for reactions, and if defense forces move in not a smart way, to burst inside the system, in the attempt to get in or make it look like so the defender means lose their delta-v, main forces fire where u not intended to be, etc.
it looks like u have a healthy setup so a healthy attitude to all that, and it is to your advantage.
Depict what u think is sensible and meaningful - keeping in mind that development advancement in warfare never stopped in human history(hand in hand with technology, our capabilities) - so if u need a victory of someone nothing stops u to improve combat system u have, have more advanced strategies and setups and less advanced ones and u can change and investigate them as long as the show goes on, by changing times and places.
I have seen people who spend way too much effort on realistic combat strategies which are easily countered by some different and quite obvious strategies. As u may have seen through my taste - my current understanding that missiles with good engine and understanding that ships==missile, a cloud of wreck==missile, rail gun, gas cloud==missile - mm haven't seen strategies which would really put a significant dent in that strategy. I'm the first to admit it has its cons as well, and certain difficulties, it isn't absolute - but all that situation dependant - basically what u would like to have for story building.
some random points to address
With such powerful, fast, long-ranged weapons, what tactics can you use? What strategies can you employ?
- overwhelm u opponent - u have a whole galaxy resource to build up muscles, if they do not care what happens around them
- be sneaky, be smart - infiltrate, corrupt, hack, make diversions, lie about u goals
- one does not negate another
On the strategic scale, I would imagine a lot of maneuvering to happen before anyone committed.
- dragging time is the defender's advantage, if the attacker does not have overwhelming sufficient force. An attacker is a knife - it has to hit fast and strong achieving results, or run.
...combat happening over interplanetary distances..
- nop, but u have to keep an eye on your system presence to your adjacent system 10-100ly around you. Enemy rooting there will be your future problem. And with the lone star system, u will be toast faster than in a day after a decade of enemy preparations.
All the while, 'spotlight' sized lasers, and sprayed macrons & particle beams create a 'burndown' - even if one can continually dodge UREBs, SNAKs, pulse lasers, casaba howitzers, or tight groupings of macrons, there will be constant damage.
- I like that mess, it smells like an epic fire to burn, borgs approve. But as result u can handwave any - they grinding each other, so the outcome is defined by luck and skills and small differences in tech, and forces. if it lasts too long defenders win.
dogfighting in smaller groups
- throw that away, a gas cloud of an exploded missile will wipe those guys in an instant. The only good depiction of that was in some of the StarTrack blockbusters (do not recall which one) where at the beginning there was some alien tech, some swarm of small ships which hit down the discovery. That was a good use of small crafts - as the mean to hit a big ship.
For an attack, would one try to stage out firing slower weapons first, ...
- for defender fastest attacks first, soften the target, exhaust its resource. put them in a bubble so they do not see what u do.
- for attackers first is most likely powerful and(or) versatile - they have the time to build momentum, they select the opportunities they prepare for the specific defense penetration. All sacrificial sleeper agents start to act.
Lasers are overrated - take look at a recent problem, especially comments about what it takes to kill a raccoon - Wattage of Laser Rifle - it takes 100's of kJ to kill a racoon when other means do that for 50 or less.
Some of those ideas still hold in terms of evasion how and why - Flak(1944) - it just 3d for space and each time someone is forced to do evasive maneuvers is a loss of reactive mass and delta-v - so forcing the other side to do that more often and for longer period of time is a good thing.
This one is very conceptually insightful, it needs mediations - This AI Does Nothing In Games…And Still Wins! - a seed for modern ai's and space - the art of war. But it is up to u how much u can gain from it.
Splitting the question may not necessarily help as the battle system is variable sensitive and thus has to be considered more or less as a whole. But at the same time, u almost never can be wrong(or right) with it. Can some ships fight at 1km range - yes they can. it is stupid - yes it is. but can they? - yes they can, reasons are plenty. is it possible to imagine better strategies? - yes. is there an absolute strategy? - no.
And u can pick any of the possible as one exciting at this time and all that, even if it is the worst one. what do u need is just to avoid sht pits - like making water be a problem on ceres - with the abundance of hydrogen(gas giants, sun) and presence of stone it can't be a problem, especially with recycling which is the must anyway. So it more on the strategical side of things.