Hey thank you for your review! I really like the Idea of creating a Level to introduce each of the Units as you said. A level where the use of this special Unit is crucial to win and I'll try my best to do so. Then I think I'll keep the choice for the player to Unlock them I the order of there choice.
I can make it a way of earning some Gems and learn the special weakness and strength of a given Unit in the same time. Love the Idea !
For the Stats it's coming in a way or another I'll give some information to the player about his units but I didn't thunk about giving score on each unit type. I might do that as well.