25 (or 24) of anything is a mistake, imo. circle of healing truly is godly in large numbers (5+ priests). the minor sacrifice in AoE DPS is made up by the fact that nothing except serious, numerous focus fire on single mages will kill them.

if it were my setup, i would be looking at 15 mages, 5 shamans, 5 priests. one shaman, one priest per group. i would also spec the shamans for resto. run in alltogether with shields/earthshield precast, drop totems and stack your healers ontop of them somewhere reasonably safe, but within line of sight of your mages, then put your low rank chainheal/circle of healing on "toggle" with your G15 and forget about them. (except to press your hotkeys for changing the group focus of the heals) while you run around with your mages on /follow and kill everything in sight.

think of the 10 healers as a moveable unlimited HP turret.