Re: [M&M 2nd ed] Freedomverse game?
I'd start with one. If you get a good response, active posting, you feel yourself energised enough... start a second.
Hard cap though. Doesn't have to be a small hard cap like 4; but the moment you start going "Well I was going to stay with 6, but there were too many awesome concepts..."
You run into problems, in my experience.