On setting design, while bottom-up is a good principle for the physical bits (planets, characters etc.), I would advise the OP to think through some of the basic features of his setting first. Like, do you or do you not have FTL comms? Otherwise you risk something like the following: after a few weeks of happily tramping speculative freight around the Five Suns Federation, it becomes plot-necessary to be able to place a call to a different system. Fine. Next thing, someone asks: so this cargo we're being offered... why not call up our potential destinations and get quotes there? Maybe even lock in a price?
Puff goes spec-trade campaign.
How FTL travel and comms work (if at all) is probably the key question to answer. Plus, is the economy post-scarcity (via quasi-magically-good nanotech or whatever)? And, how good is neuroscience - can you upload personalities? If so, physical death becomes less of an issue.
Oh yeah, and probably: are there aliens, and if so, what tech level and what degree of physical / political power? If there are aliens roughly comparable to humans in tech and military power, I think it's much more likely that humanity will be organised under some sort of unified government.
Random suggestion: one of the SF backgrounds I've liked most recently is Hinterwelt's Nebuleos. The thing I like best about it is that humans are the oppressed underclass of the setting, rather than the dominant players as usual. Straightaway made it fresher.