Majestic robe set and a 2 hand A staff. Get WIT tattoos to increase cast speed and m.crit chance.
After lvl 76, your Weapon Mastery will have "a chance to absorb 1% of damage dealt as mana" 2% at lvl 80 and so on.
Assuming you bought Hero starting packs, you should have plenty of accessories to increase your mana regen on top of that, so your mana should never deplete.
So you select Steal Essence, turn on Warcry, press Autofarm and go afk.