I never got involved directly with RPing on the Citadel in the past, but I observed some of it and did a substantial amount of different RP's on another site. The ones we did on the other site were all single threads (I don't exactly understand how you manage a multiple thread RP). One or two people would come up with the initial RP scenario (the DM I guess? We never used that term but I guess its the same thing), people would post bios for their characters and when it had enough sign ups the DM would make a new thread (the actual RP, separate from the signup/discussion thread) and begin the story. Everyone would be pretty much free to start in their own locations and go in whatever direction they wanted, but the DM would push the major story forward by introducing events, sometimes outside of their own characters prospective. In some RPs character interaction and groupings happened naturally, in others it was forced by the DM.
OOC discussion would happen to help guide people or debate a certain issue, but usually we just let it flow naturally. Some DM's pushed a story arc harder than others, but either way they mostly worked out. People dropping out was an issue, especially if that character was critical to RP, so other players normally picked up discarded characters to keep things going. Not all RPs were successfully, but we produced some bloody good ones and they were all a lot of fun.
I'm totally up for creating an RP subforum if it's something you guys are interested in. The only reason it didn't come over from the previous board is no one was using it.
EDIT: I'm also open to not just doing FF7 RPs, although I'm sure that's what everyone has the most shared interest in.