Need Help Balancing Castle Defense

I Don't have a problem with anything but balancing, and coming up with more ideas.

I have attached a map called castle defense that is really old, and that i have been working on updating. I working on balancing it atm, but I'm not good at it.

I'm willing to change any of the wave creeps health, dmg, number that spawn, types that spawn, spells they cast, any of the heros spells, health, items etc.

Map attached is unprotected if you want to change things yourself, but I can do that own mine own if you just come up with the stats/ideas.