Actually, in the beginning, 1 character judge is enough. It's when things start to get momentum that a second character judge is needed (speaking as someone who has seen the deluge of mails that a character judge has to deal with at times).
I'd put my mark at 20, maybe 25 votes, to allow for the inevitable dropouts on all three fronts (player, DM, judge). Judging by the response so far, those should be coming shortly.
I agree, from what I know, Alien is by far the hardest to justify with the currently preferred setup, with only a few rare possibilities. Disallowing it, at least for the start, may be good.
Kylara, what power sources are used as examples in M&M?