I'm level 2x now probably stop at lvl25 to decide before I go forward with it. He's current setup you can see in this but he is killing 2-3 monsters before heal or regain so if I go +int I'll heal a lot more and more damage than now? Funding for this is not much of a problem but not crazy amounts.

Level 35 or 40 in my opinion, this way you have enough mana to do some mobs and you can kill fast enough. Of course if you want you can start casting at 25 you will just gain about 3 mobs also, depends on you're preference. Most people start 35-40 casting

Caster from 25-35.

It all depends on your gear though.

I used to start from 25, but my melee gear overpowered the casting gear.

Now I melee to 30, and cast + melee to 35. Full casting after that.