No, I don't think they can (or rather will) be placed in a system without a star. They are placed just like any other player. Of course you could change that. Just place them wherever you want on a custom map.
As for the sensors, sure mod anything you like
. Might be a good idea to change the AI files a bit then and build some WeaponPlatforms, Troops, Defense Bases, etc. (make designs and include them in the contruction list).
Rollo