"I am thinking of being able to upgrade the warrior to a knight for example to get buffs of like 25% to all stats etc" You should propose differents classes to chose from.
Ok , after thats i playing a little time full upgraded and i have to battle with one immortal kamikaz , i stop , i don't wan't to be ban for this game and i don't think it's fun if you can have the full power at the start.
 "Tap Heroes"){kind=icon}
 "Anti-Idle: The Game"){kind=icon}
 "Wooden Path 2"){kind=icon}
 "Monster Slayers"){kind=icon}
 "Bunny Flags"){kind=icon}