This seems like a pretty good idea.
Bureaucrat - 5 - 8 (8 if the wiki gets more activity)
Administrators - Not including bureaucrats, 2 - 3 (since bureaucrats are admins already)
Rollbacks - 10+ (If a user has a need to revert easier, then so be it)
CVU - 3 at most, the wiki doesn't seem that much active as it used to me :(
Chatmods - 1 - 2 (Chat isn't that active anymore)
Helper - Well, I used to run this group, and I only used it when I really didn't know how to do something. So zero for now... but if you guys need it then I would seek some help with advanced users, as there is no need to grant someone adminship and call them a helper.
Bots - Just create them if you actually need them.