I know this is an old post, but I'll add to Teatime's rundown. Apologies if you're already aware.
Up to 18 elements in a Division (this includes the Leader) but there is also a limit of 15 individual units + a Leader in a division as well, so effectively 16 elements if using single element units...Now I haven't tried this, but there is a setting in the GameLogic.opt file that specifies the number of subunits.
subMaxNbPerUnit = 18
If it's possible for the end-user to change the number of maximum elements in a combined unit (i.e. division) that's where I'd expect to find it. However, there are settings in CW2 that you can alter that don't cause obvious errors but still don't get the result you wanted. I don't think I've tried playing with that setting yet.
There is no limit, that I have found, to how many divisions you can createI don't know why you'd want to, but you can add a limit to the number of divisions and corps with these commands: SetCombiUnits, SetFormedCmdMax. CW2 uses a combination of the two. According to the wiki (
http://www.ageod.net/agewiki/SetCombiUnits), SetCombiUnits can or did handle all three but now CW2 uses it to set the number of divisions. SetFormedCmdMax is used to set the number of corps/armies.
Another setting related to divisions is ldrCommandCostCombiUnit, which supposedly sets the CP cost of a combined unit. So instead of it costing 4CP to form a division, you could make it higher or lower. I would love to see this changed to make the combined unit CP cost at least somewhat related to the size of the division.
The number of corps attached to an army is limited by the leader (think it is related to his strategic rating, not sure on the exact relationship) I'm not sure this is the case, and I don't remember AACW well enough to know if it was the case then. At least I haven't found where you can alter it, and you can change quite a few of the settings related to the corps/leader relationship. Most of them fall under the COMMAND AND LEADERS section of the GameLogic.opt file.
jm