Chloro mages are very decent for healing and damaging, just keep in mind you can also do the same with rogues and cleric classes as well with certain talent specs.

Warrior + Mage Setup is similar setup to another player on Wolfsbane, i think he is in the process of switching mages out with clerics i believe. I personally love the idea of a Cleric Tank + 4 Harbinger (Melee Mages), one day i may get there.

Also the first instance for Guardians is upper teens 15 x 5 is still a bit low.