[Ygorl]

I've found that, just by forging a clam when I've got spare water gems sitting around (i.e. no queens to summon, no boots to forge, all the global slots are filled, no nifty artifacts to make, etc...) it's not that uncommon to have 20 or so by the late parts of the game, on smaller maps than this. If we do just a hard cap, I'd prefer it to be 20 for the gem-producing things and 10 for the soul contracts. I wouldn't mind limiting vampire lords too, but the only because immortal vampire hordes are boring, not because they're particularly overpowered.
This is just my vote, though. Lots of other people involved in this game, probably most of them more experienced than I.
Cheers!