Re: Team size
On topic with respect to playing, I prefer to limit my group sizes for games depending upon both my familiarity with the system and my players familiarity with the system. I think trying to run a Champions combat with 7 or 8 players who are not very familiar with the system would be very slow and probably very difficult to keep up the interest of the individuals while waiting for their turn to come back up again. With seasoned players, I think that 7 or 8 would be possible with about 5 or 6 being near the top of being able to consistently handle everything smoothly. But the "ideal" minimum would be largely dependent upon what you personally look to fulfill with your gaming time.
On topic with respect to comic books is another matter, IMO. The larger teams (10 or 12) should probably overlap but have differing comics. If you go ack to Shadow Hawk's tvtropes division, I think that you should also stop to think about whether or not there is a character who often acts alone and how often the group will be written so that it splits up. Infiltrators and vigilante types often act alone and yet can be vital to a group's success.
If a plot (and thus the heroes actions) becomes more complicated, they will need to split up. So, you would need to determine whether or not they have enough members and a skill diversity to break into multiple self-sufficient groups or multiple groups some of which may not be solid teams.
I guess another thing to think of is whether or not this is something you are interested in actually using to build a following of readers. I think that readers will often identify more closely with one or two members of a team as favorites. If you start with a large team I think it will be difficult for readers to get enough of a particular character to develop a strong interest before they get bored with it and find something else tospend their time and money on. So, IMO, starting with a smaller team of from one to three and then adding a couple to show the team's creation or just starting with four or five or so and developing them all in depth would be better than a big team. I think it might be easier that way for a reader to go "Ooh! A new guy, what can he do?" if the reader sees an image out of a group of three to five a cell of just one hero than it would be to think that out of such a large collection.