Just a couple of quick questions (and as simple as they are, Google failed me):
Is there a limit on how many member groups I can create?
Is there a limit on how many sub forums I can create?
there is a master internal limit
as you create a new group or a new board, the internal counter associated with each increases and is not decreased on deleting them - in both cases i think the limit is 65,000 or so
there is a limit on how many groups a user can belong to at once though, thats much shorter but not fixed, typically caps at 100 or so depending on circumstances (the list of groups a user belongs to is stored as a string, max 255 characters, in '1,2,3,4,5,100,123' fashion)