noticed this thread been here for a while, and I would say there is two simplest ways to make a sci-fi rp and that's a Merc group, or some kind of special galactic forces. Merc group is a lot easier to deal with sense it's more open for possibilities while the other your kind of limited to good only. either way would accept special jobs/missions from various factions if a merc group, otherwise from the governments of various planets, which members could decide if they wish to be on the team. even make it where every roleplayer has chances to create their own missions and everything, even allow multiple missions to happen at same time.

When it comes to Sci-Fi rps I think I've have more experience than I've had with other roleplay types sense I had a group who purely did Sci-Fi on another site.

The actual Merc ship/compound or Special Forces ship/compound where everyone lives would befairly big, if it's a compound/spacestation/what ever, then it would have shops and stuff but if it's ship then literally just a mobile home. which who ever is the GM would have to control where the ship is at any given time so would have to make it stop by planets and space stations for various reasons.