Sosostra's prophecy lead me to a chest with pretty crappy loot.
I didn't get a mage head for my creature until I was level 16, from one of the chests in Lovis' room. I had reloaded a few times there at level 10, but was only offered a warrior head, so decided to try again later.

AFAIK the ghost summon will concentrate on healing if it is safe, and possibly cast a fireball if not. Joram has recommended turning away from opponents before summoning the ghost to keep it behind the character (so it doesn't get targeted, and will focus on healing), but if attacked I don't know how much it will use the fireball spell compared to melee attacks.

I described my playthrough with a ranger (with a little bit of unarmed combat early in the game) in the topic Who's playing DKS on nightmare difficulty ?. Joram and Senior Cinco also described their games, but not playing warriors or battle mages. Stabbey did a very detailed 'Let's Play' for an unarmed monk character in another forum.