I can't really comment on that middle question, but I'll still answer on everything else.
1. GMs, no matter what faction they pilot, will always have to deal with factions that aren't their own at some point or another. Limiting the creative process will not do much to remedy the alleged disconnect between GMs and FMs. I say alleged because I haven't experienced this myself, clearly.
2. Active, yes. GMs - see response above
4. And one offs add to the spice of the rich canon of the SARPVerse without needing the rigid structure and organization it takes to be an FM. Of course, both PCs would have to follow certain aspects of civilization (permitting backstory, etc. This part is kinda silly to mention, really). I say let out-of-plotship RP stay.
1. GMs, no matter what faction they pilot, will always have to deal with factions that aren't their own at some point or another. Limiting the creative process will not do much to remedy the alleged disconnect between GMs and FMs. I say alleged because I haven't experienced this myself, clearly.
2. Active, yes. GMs - see response above
4. And one offs add to the spice of the rich canon of the SARPVerse without needing the rigid structure and organization it takes to be an FM. Of course, both PCs would have to follow certain aspects of civilization (permitting backstory, etc. This part is kinda silly to mention, really). I say let out-of-plotship RP stay.