Cosplay manager here....
HAPPY NEW YEAR (this being written on New Years Eve....)
We are working on tweaking the rules (which is why I am on the computer at this date and time - it's one of the few times I actually have free to do personal stuff), however certain things likely are not going to change:
"Skits for 1-5 participants shall be no longer than 3.5 minutes; skits with more than 5 participants may be allowed up to 5 minutes for performance, at the Cosplay Coordinator’s discretion."
We've never officially stated a maximum number of participants, however I think that the Hetalia group a few years ago has 12 people and that made for a rather full stage, so you're better off keeping the group smaller...besides, it gets exponentially more difficult to coordinate larger groups to get together for rehearsals and suchlike, so keeping the group small is advised.
Rules will be provided to Programming (Jaki) at the January Kumoricon meeting, and I expect that the Webmaster will post them shortly after she has approved them.