i'm speaking from my own experience here, and I think that we should take a look at the big picture first before filling in the little details.
so we're obviously not in the milky way galaxy anymore, what galaxy are we in? how many worlds/planets will we have... of course, we need races for our players... then we can go on to determine smaller details like the other inhabitants of the planet(s) and such...
correct me if i'm wrong, but i don't think we'll make it to the online stage anytime soon, so let's make this a single-player type... first or third person, i don't mind either.
I think we should have the protagonist be an actual human, let's say that Earth is having some issues (cause we all know that it's not ...*cough*...) and they sent a team out to space to find a new home for the human race. So they come across a nearby galaxy and something unexpected happens, the crew goes missing, and there's one guy left and that's the main character. Apart from him everything else should be quite irrelevant to the planet Earth.
Anyways, just my opinion there... something that I'd like to work on. Let me know how you feel about it!