Once you get the Belt of the Aleroth Archmage (and any other part you desire, since alone it does nothing) mana is never an issue, so don't spend *too* much on Spirit.
Don't like firewall or fireball. First is too dangerous, rather make a run if enemies get too close. Second just isn't as powerful as MM. Destruction is always welcome, and use Battle Mage once the penalty is reduced or even giving bonusses!