Right now you can only get 4 Cheese relics, but you might be able to get more in the shop, and then there are 2 cards that give mana. There is no hard cap on max mana right now (and there will probably never be). Im planning to add more relics that increase max mana but all of them (including Cheese) will have some kind of a draw back cuz +1 max mana might be a bit too strong for a relic