Gravity well warp Restrictions.
Stops Space ships from just appearing next to your planet i suggest a ring around Each system that forces them to stop at the edge of and to move through the systems!

In between system obstructions.
Ships cant straight shot trough the galaxy they have to zig zag around items,
or even go in a 90 Degree approach angle around a nebula or obstruction in the way or can choose to take random back and forth maze like paths through whatever it is and find war fleets!

system obstructions.
ships have to go around to an entrance point an asteroid belt
and asteroid don't let star ships just hover over them unless there construct or small enough because of Electromagnetic force from the star (Is real by the way anything in the south pull or north pull is Messed with Fairly bad.. (this is why we don't seam to have any satellite Pictures of the solar system from Above. like from 3 orbital rings away Or 2 light minutes away (so if it matters its a real thing) so you should not be able to just fly ships into asteroids
and there should be Walls or Even natural Phenomena (like the electric storm outside of earth there)

Actualities.
Actual asteroid belts! more realistic Planet (Saturn) rings with a couple mine able asteroids
and more useful Phenomena that cause science points and other things!
distances and sizes.
Planet sizes and Star ship sizes should be changed around to look as realistic as possible as well as Planet to planet distances!

these don't sound too hard anyways!