Hi,

I like smaller groups myself, and think 4-5 maximum per team is good enough. It also ease the reading of on-screen action, and GUI managment for healers mostly, but not only.

As for group of groups, i think Rift did that for world events, and Warhammer online too (not sure, my souvenir is vague about it).

I like mentorship. Higher levels can support lower ones, but also lower levels can join higher levels for adventure. City of Heroes did a great job for finding group, joining, having purpose, and it was actually my favorite MMOG for group content. We even ended forming a guild from grouping often with the same "random" players, and we played together several months like so. Dah, i miss this time...