I wouldn't try making a pure mage until act 2 (actually I wouldn't try at all, personally, but if I was going to play a mage, I would wait until act 2 before expecting much in the way of magical combat effectiveness).
Give the act 1 doll a crossbow, set it to aggressive, and make sure you summon it out of the way of any expected opponents. It is fine kept away from melee fighting. Later in the game switch to power arrows whenever you can, or splitting arrows for groups of opponents in confined spaces (where there are no friendly NPCs or creatures around).
Playing on tactical, I only bothered using the skeleton doll for combat for the occasional tough fight.
