Wow, I leave for 90 minutes and people have a discussion without me. ;)
OK, first things first.
We're looking at only having Jump Engines on ship of size class Large or higher. Right now, that's 5,000 tons or better - about the size of a small destroyer, (That's the lower limit of 'Capital' class in Star Wars. About the size of a Corellian Corvette ... over 100m long ish) We could also include a restriction by Tech ... like Tech 6 cultures have to be Huge or larger, Tech 7 Large or larger, etc. That seems needlessly complex to me, but I offer the idea.
I'm thinking we'd only use Star L-points - points between stars and major planets. (not Pluto planets).
L1 is sunward, L2 is on the far side of the planet. L3 is opposite side of the star, L4 is leading (I think) Trojan and L5 trailing Trojan. The L4 and L5 points (I believe) aren't as stable as the others; (things caught in them tend to take up kidney-shaped orbits rather than just hanging around) L1 and L2 being the most stable.
Any planet will create L-points with its star(s). Yes, every planet and solar system would have hordes of L-points at different distances, modified by moons, binary stars, etc. Most moons don't have enough mass to affect a planet-star L-point ... they're just too small. (assuming the planet in question is relatively large, anyways). More on that later.
The risk of one 1 km long starship colliding with another in the volume of space represented by an entire solar system is miniscule. Maybe if you were all jumping in together near a planet ... otherwise, it's no big threat.
Suggestions for Jump Gate locations:
Star-close: I have to credit my Dad for this idea. We just drove up to Fayetteville, and he and I were discussion this sci-fi problem. He mentioned that if Jumpgates take a lot of power, that locating them deep *in* the system might be a good idea. Lots of easy, cheap, powerful solar. Same for Jump engines ... it's easier to exit hyperspace in a deep, deep gravity well than in 'normal' space. Turns the normal jump tech idea on its head. I thought it was interesting so I'll pass it on.
System Edge: The already-discussed system-edge idea. The thought being that beyond your last major planet's orbit, there's less trash to run into, little traffic, and it's easier to enter/exit hyperspace well away from all the gravity wells.
Planetary L-point (L1): Jumpgates at (major) planetary L-points; the L1 point has uninterrupted solar exposure; this might be a good standard for the L-point jumpgate idea. However, Greg has to make a program to figure distances for the math-challenged like me. :)
Gas Giant L-point: This is my favorite. Considering that it appears that any system that's going to have habitable worlds needs a gas giant 'trash collector' further out in the system to protect it, maybe only the Lagrange points between something with the mass of a gas giant and a star are large enough/stable enough/far enough from unshielded people. Once again I'd favor the L1 point though there's no reason you couldn't use them all. They only thing they'd be 'close' to would be moons; even then the L-point is likely to be what, five times as far away from the giant as its moons? (That's a rough guess, I know it has to do with complicated math concerning the mass of the star and the planet and so forth, but I'm on vacation). That's a good long way from most everything.
- "Don't assume you are safe because there is a rational explanation for all of this."