I've had this story sitting for a while, but decided to come back to it. I plan on skipping ahead a few decades, where I have a giant space fleets. Assume that the ships are made for humans. Any repair crew, reserve pilots, etc, will be on the Flagship or a planet military base.
Here's the basics of a fleet-
Gateway- a large apparatus equipped on every Flagship capable of transporting an entire fleet across the galaxy in a matter of seconds.
Flagship- several times the size of the largest Frigate or Destroyer, Flagships are the main module of transportation in emergencies and quick responses thanks to their Gateway abilities. Heavily armed and armored, their one flaw is their inability to do much of anything about an hour after using the Gateway. For this reason, ? Frigates and Destroyers are always nearby as an escort, as well as ? squadrons of fighters. Not capable of in atmosphere flight due to its immense size. The quad hangars of the Flagship, located on the top, bottom, and sides of the ship, are capable of holding ? Fighter squadrons each as reserves or a defense force.
Frigates- large gunships capable of space and in atmosphere combat. Bristling with guns and well armored, their main purpose is as an escort or support unit.
Destroyers- incapable in atmosphere flights, Destroyers are specifically designed for attacking large ships. Fighters can be taken down with smaller turrets along the length of the ship, but large forward guns with a slight range of movement are the primary weapon against larger units. Usually paired with Frigates when possible, allowing the Destroyer to focus on the larger targets.
Dropships- usually smaller than Frigates or Destroyers, Dropships are used to ferry troops and supplies wherever they are needed. Lightly armed and armored to maximize payload, an escort is always needed. Larger versions may carry a Fighter, but rarely do as the needed supplies and maintenance crews limit the rest of the cargo.
Fighters- single pilot ships with fast speeds but low armor and firepower, Fighters are designed to be ignored in combat, but can inflict major damage by skilled pilots.
Burn Engine- a faster-than-light speed engine that is equipped on all ships, although Fighters have a very limited range. The fuel is common on all planets, allowing for easy refueling.
Frigate Destroyer attack- performed by a minimum of one Frigate and Destroyer, the Frigate(s) line up slightly in front of the Destroyer(s) and fire all guns at once towards a single target. The Frigate energy beams phase together for added range, and clear the way for the Destroyer beams by obliterating any smaller ships in the way, with any remaining beams severely damaging shields on the target vessel. The Destroyer energy beams fly inside or just behind the Frigate beams, and deal massive damage to the target vessel. The downside of this is that all participating units need to reload.
I need help deciding the numbers for the 2 ?s in the Flagship description, as well as the numbers of Frigates, Destroyers, and Fighter squadrons for the rest of the fleet.
EDIT- TheDyingOfLight pointed out that Fighters are almost useless, so I'm gonna change them to being too small for targeting locks, and being remotely controlled from pilots on the Flagship. I should've done this before, but better late than never. The main purpose of the fleets are mainly defense against external forces, but also as a sort of intergalactic police force.
EDIT 2- The fleet size and amount of ships seems dependent on a variety of factors, so I'll try to go into detail on their purpose.
When they first began making spaceships, there were no Gateways, but there was Burn Engines. The first purpose was as a defense fleet, not made to win wars, but stall an enemy fleet until the planet, or at least most of it, could evacuate. The evacuation ships would be armed, but weakly armored and equipped with Burn Engines to get away quickly. Once the evacuation was complete, any remaining ships from the defense force would follow.
After a sizable force was built up of about two fleets(please note that a fleet is not the entire space navy) they began to act as a sort of intergalactic neighborhood watch, mainly stepping in when humans almost killed themselves and keeping non-military pilots in check(i.e.- stopped smuggling, unlicensed exploration, etc. ). After this, Gateways came around and were incorporated into each fleet. Because they were so large, Flagships had to be built for this purpose.
Where I plan on picking up the story, they act as most of the space force of the galaxy, mainly for defense against enemy ships if they ever showed up. Earthlings have a smaller space force, but not nearly as advanced as these ones. Some fleets are specialized, either for ground takeover(More Dropships, Frigates, and Fighters, as well as ground troops and supplies), and ship to ship attack(Less Dropships, but more of everything else). The majority of the fleets are all around with all ship types, and a varied cargo manifest.
As for planetary defense, most planets have an orbital defense grid, most commonly equipped with mines and proximity alarms, but some versions have drone fighters, stationary missile launchers, shield generators, etc. Once you get below the defense grid however, the only defenses will be ones on the planet's surface. When attacking the planet, you do not need to take out the entire defense grid, only your attack point, but prolonged sieges will need more or all of the defense grid destroyed.
When I continue the story, I don't plan on assaulting a planet, mainly orbiting shipyards, but these would have their own exterior gun turrets. Capture is not an objective, only intimidation, so Dropships and ground troops wouldn't be needed.