I'm trying to figure that out, actually. I don't think I can run two groups, honestly (Dungeon Star taught me that my ability to handle large amounts of people is... limited).
I think I'll be looking at... 6, maybe 7 people tops. And I might have to put some downright draconian rules, posting-time-wise, to keep the ball rolling.
I'd hate for this to stall to death. Admittedly, last time was my fault.