It seems fairly reasonable, but I have a couple points to make. It's a bit long-winded, sorry.
First, there's no such thing as "outside" a solar system or planet's gravity well. For practical purposes, gravity wells are infinite, but decay exponentially with distance. Every point in space is under the influence of lots and lots of gravity from the billions of stars and planets around us. You could say the wormhole only works when the net gravity is less than some value.
But if you allow the wormhole to work between the "edge" of the solar system (e.g., Pluto's orbit) to the more civilized areas (e.g., Earth's orbit), there's really no reason you couldn't jump from anywhere in the galaxy straight to Mars' orbit. The difference between acceleration from the Milky Way in deep space and acceleration from the Sun near Mars (about 227 microgees) is considerably less than the difference between acceleration from the Sun near Pluto and near Earth (about 605 microgees). You'd still need to be away from the planet itself a little ways, but we're talking hundreds of thousands to a couple million km, which is a stone's throw in cosmic distances.
I would suggest (if we assume most habitable star systems are similar to ours) that you establish a baseline of something like the asteroid belt, and you just can't jump inside that range. It would still take hours to weeks at sub-light speeds (depending on how close to light-speed we can get) to reach the inner planets, while allowing jumps in the outer regions of the solar system which are huge. Also, this means you couldn't get closer than roughly the Moon to a planet, even if the planet is far from the local star, and big planets like gas giants would be farther.
The basic rule of thumb: take the farthest naturally-habitable planet from the local star, double the distance; you can't jump anywhere in that radius from the star. Take the farthest significant moon from a planet, double the distance; you can't jump closer to the planet than that, even if the planet is well outside the star's no-flight zone. Not quite scientific, but it's reasonably close without getting bogged down in math, and it means your defense forces always have some lead time to get prepared.
Second, the very idea of a wormhole is to bypass the straight line. You essentially create an entirely new tunnel through a higher dimension that is much shorter than the regular path. The wormhole intersects "real" space at its end points, but is totally outside real space at any other location.
However, I suppose you could say the wormhole tunnels parallel to realspace and is just extremely dilated spatially. Then huge gravity wells might reach out across extra dimensions and interfere. This would also allow longer realspace distances to correspond to longer wormhole distances.
This means you wouldn't be able to make a jump from one side of a black hole or other supermassive object to the opposite side, but the angular size of the object at the distances you're allowing jumps makes this a pedantic note. You could choose a random jump direction every 5 minutes for the rest of your life and the odds of accidentally trying to jump through a star or black hole are pretty much zero.
Third, there would be no feasible way to predict a ship's jump path, move your own ships to an intersecting line, then activate your super-gravity generator before the ship was long gone. The only time such a thing would reasonably work is if you were disrupting a well-established trade route, or knew ahead of time the exact path someone planned to use.
Fourth, some additions to the trade routes idea. I would expect that most ships would have no wormhole capabilities, and would instead rely on fixed jump gates. Star systems would likely have massive wormhole nodes, much like airports, and people would simply fly to the node, pay the appropriate fees, then fly through the wormhole when it's their turn. It could even be like a traffic light, where the wormhole is opened to one destination for some period, dozens of ships fly through, that portal is closed, then another is opened to a second destination. Repeat for each of the local star systems.
For large, wealthy systems, the wormholes would be open almost constantly, and you'd have very little delay before traveling. For smaller systems, you might have to wait several weeks before the next scheduled departure.
Also, the wormhole network would likely have a sort of hierarchy. So you'd travel from the less-populated star systems to a regional hub, then from the hub to a different local star system. Then you'd have super-wormholes between regional hubs. The super-hubs would likely be spatially separate from the regional hubs for security but don't have to be.
All hubs on the wormhole network would undoubtedly have very intense security sweeps and so forth. All ships would be checked for illegal / dangerous cargo, dangerous cargo would require licenses and permits, all passengers would require the appropriate passports, etc. Military and/or security ships would be everywhere, and the entire hub would have some type of shielding to prevent unauthorized wormholes in the vicinity. Perhaps the shielding has some kind of "signature" so you can bypass them with the correct key (probably just some physical property, like the frequency distribution of the shielding or something). Then the station operators can tunnel into and out of the shielded areas, but others can't. This caveat would allow scenarios where terrorists or mercenaries could bypass shielding, but they'd have to gain access to the shield key first. The difficulty of doing so would determine how rare such events are.
Under this setup, only very wealthy people and governmental agencies would have their own wormhole drives. More advanced cultures and star systems would have a higher proportion, but cost efficiency would likely mean the only reason to use your own drives is if you're going somewhere far off the beaten path.
Also, individual planets could have local wormhole facilities for interplanetary travel within a star system without leaving the surface. You'd probably still need to be in a spaceship of sorts to launch through the void, and the wormhole ends might need to be created in a near-vacuum. This would prevent people from just teleporting around. Also, the ability to create the wormholes so close to the planet could be very expensive and complex, so only a few planetary wormholes would exist.
Finally, with communication nodes: I would suggest that even small wormholes are fairly expensive, so most people wouldn't have personal superluminal communications. However, interplanetary networks would exist, so you could talk to people on other planets in nearly realtime as long as you're connected to the local sub-light internet. Many to all spaceships would be equipped with superluminal communication, but the ranges could vary. Most ships could at least communicate within the star system, but only sophisticated and powerful communications arrays would work in deep space.
Alternately, there could be repeaters near major planets, moons, and space stations. In this case, most ships would communicate at sublight with the repeater, which would relay the information to different nearby hubs. Communications this way would have delays of seconds to minutes unless both ships were very close to the repeater. Again, expensive ships could still communicate via superluminal connections at much greater ranges with minimal delay.
Any kind of convoy (a military fleet or cargo operation) would likely have one or two flagships with superluminal connections, then all the small ships would communicate at sublight with the flagships. For recon missions, a communications ship might accompany the scout ships to keep in low-latency contact with the flagship.
Also, there could be superluminal communications equipment as a movable package, so you just buy a couple packages then put them in whichever ship makes sense for the current context. They could be transported to the ground for landing parties. If they're big and bulky, it would make sense to leave them at some kind of base camp, or in a ship left in geosynchronous orbit.
