Ideas Wanted: Writing a SciFi setting...

I'm on my way to finishing Mass Effect, which has some interesting concepts in it.

1) the capability of space travel (jump-points, mass drives, etc.) was designed and built by an unknown, now-extinct race

2) multiple races in constant conflict against the backdrop of an heterogeneous environment. I.e. space is so vast and impossible to delineate in any meaningful boundary that empires and territories are porous, permeable, semi-mapped ideas more than true lines drawn in the sand. Almost like a galactic version of island hopping only no one is really isolated

3) There is an autonomous, corporate-like council that has no overt control over each race. However, the council does control access to and from jump points, (no FTL in this one) and so exerts a lot of influence over races and can apply pressure through commerce and travel

completely unrelated:

I like the distopian idea of an adrift, post-apocalypse, almost-to-extinction human race, vis a vis BSG.

Yeah, definitely start with a Points of Light approach. Make discovering new stars an exciting part of the adventure. Ever play Legend of Zelda: Windwaker? It was cool as shit to find new islands. Just take that and put it into space. It will now be cool as shit to find new stars. Players find clues leading them to lost, ancient artifacts of a bygone alien civilization. Make a handout/prop/starchart. Players eat that up. With that, you've got stories of exploration, dicovery, unlocking ancient secrets, amassing great power (i.e. alient weapons). While exploring, the players can protect vulnerable colony worlds from the ravages of alien infestation ala Starship Troopers.

But, maybe that's just the frontier. The homeworlds are oppressed by your evil empire of choice. My recommendation would be to take a nod to the implied setting in the Half-Life series. Then you can run stories that have a "rebel vs. empire" theme to them. Everything done in Star Wars just opens up for you, giving you so many new options as to where you and the players can take the story. With an evil empire, it also gives you villains whose sole purpose in life is to break down the door (or wormhole) and show up to kickstart the session back into life with a quick combat. And you get high level villains for the players to hate and everntually defeat.