I think it would be a good idea to compile a list of all the hardcoded limits in Medieval 2. There was one of these on the org as well (which I will try to find), but in the meantime Ill start it off:
Maps:
*Number of regions: 200 (Including sea regions)
*Map size smaller maps (e.g map_regions): 510x510 pixels
*Map size bigger maps (e.g map_heights): 1021x1021 pixels
Buildings:
*Maximum number of buildings per tree is 9
*Maximum number of building trees is 128.
Units:
*Maximum number of units per mod/game: +/- 500
General:
*Faction Limit: 31 (Including slave/rebel)