1. That's something I had in mind, but I'll probably wait a bit to add it since I want it to be a mid game object, not something to get early on.
2- Yeah this is good, I'll have a cap tho so you can't upgrade past the current max level Monster in the game (right now level 4, will increase next update with next Monsters).
3. Customization is tricky with multiple unique animations (mainly the ero ones) so I'll put it in the back for now at least.