With 2% mana bonus you would need mana troop lvl 17 (11%) as you need to have at least 12 % boost. If your mana troop is lvl 23 or higher, you don’t need mana bonus from talents at all.
Peters is definitely good choice, Scarlett can be good against titans (if you have room for her).
Reference: Optimal Mana Bonus Numbers for Every Mana Speed (Now including Ninja Heroes)