The more I've been looking, the more I am under the impression that there are very few resources around that address setting up campaigns or creating settings for space games. Stars Without Number having tables for randomly rolled planet seems to be mostly it.
I guess the openness of "sci-fi setting" plays a part in that. Asking about advice on creating a sci-fi setting is too open to give any kind of answer to.
Traveller, Space Opera, Spacemaster, Star Hero, and GURPS Space all provide world generation rules, as well. Cepheus Engine uses Traveller's methodology. Each has certain setting tropes baked in. Star Hero and GURPS Space both provide discussion of adapting. Traveller and Space Opera both provide for larger setting structure (the sector and, in Traveller & CE, the Subsector).
Mekton II's supplement
Mekton Empire provides a setting pregenerated, but with the worlds not assigned to the locations on the map. (one needs to read it carefully to avoid certain issues. Note that the rules within have been superceeded in Mekton Zeta & Mekton Zeta Plus, but most of it is a setting. MZ itself discusses setting issues about running anime.
Star Frontiers had no system gen, either, but included a setting with a 21 stars and their inhabited worlds laid out neatly on a table and a map... Knight Hawks added a map that tells you just how long it takes to get from a to be... a bit cartoonish, really, but intended as both RPG and boardgame. Zeb's guide adds more systems.
Every game mentioned above is still available in either legit PDF or in dead tree.
And every one of them bakes in assumptions intentional or not.