I would go mage over wizard. Wizards dont have sustained damage output until very late game with clickies. Mage basically is the benefit of nukes while having consistant melee dps from the pet.
Any healer would work well for you. Cleric is ofcourse the most straightforward choice but consider ports from druids or buffs/slows from a shaman. Cant go wrong with any of them. Have them pick their favorite
The bard vs Enchanter argument is interesting but i would say that enchanter will outclass the bard for general grouping purposes. Youll get charm dps, the reliable cc and the mind buffs / haste. Bards offer similar benefits albeit less potency over all. There is some credit to being able to cc 20 mobs with aoe snare though. High elf is the technical best race for enchanter and half elf for bard but mostly wont make a difference. Human bards can wear robes
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Your last slot could be viably filled by any dedicated dps class. Necros have good utility if played to their full extent but a rogue brings that raw melee dps that is perfect for xp groups.