A healer would be defense guy. For an adept / mage, Improved Ability, Enhanced Perception, Natural Immunity, Missile Parry, and Rapid Healing would be acceptable powers.
Spells would include Health spells (obviously), but some Detection and Illusion spells as well. Basically, anything that can be used to protect the team and other people. Physical Barrier would be a nice one. Mana Barrier too, as you could protect the team with both. Invisibility, to hide your patient, etc.
You'd want one or two combat skills (not spells) to protect yourself, but your character would be the support guy, not the gun-bunny.