Not sure why you dont make the mage lead.
You'll benefit from all the targetted aoe, and i would think it's much easier to have 1lead+4 similar followers rather than 1 lead and 3 followers+1 different follower.
With a frost mage you'll also have a much easier time using the water elemental if he's lead.

if it's mainly leveling then you shouldn't be afraid that your mage will take the beating, most mobs should be dead by the time they reach him i'd think.