I am totally new to all of this, but here is my take:

The 1 priest/4 warlock or 1priest/4 mage combo would probably be easier to work...but I was actually thinking myself of going 1 priest, 1 warlock and 3 mages. You get all the DPS you need, a tank from the warlock, and plenty of heals.

Thats my opinion but controlling 3 different classes will be a bit more challenging i figure .