first, make sure all your mages have Cone of Cold and Frost Nova on the same hotkeys on all 3 clients. add the frost nova hotkey to your RoundRobin list. find a nice spot with humanoid mobs a level or two higher than you, preferably with 3+ camps close together that you can run between and clear. one camp wont support enough mobs and you will have excessive down time waiting for respawns.

since frost mages crit a lot on frozen targets and CoC hits multiple mobs, i think id be AoE farming with it. simply run into a group of mobs, hit fire blast on your way in (mostly just because its there and you might as well use it.. focus fire it on any named/harder mobs in a camp if there are any, to help get that mob down quicker) and then spam 3/4 arcane explosions then hit frost nova ONCE and cone of cold x3. you should crit all 3 CoC's on frozen targets most of the time.. then, if theyre still not dead, spam arcane explosion a few more times. this tactic should let you drop groups of 6-10 mobs at a time with ease.. simply run into a camp, use the spell combo i mentioned, loot, next camp. if you find a good spot you can run in circles and only need to drink every 2/3 pulls (20+ mobs). nice xp/cash, minimal down time and much less risk of death when compared to fighting elites. elites are only really worth farming for drops.. they slow down your XP too much to be worth leveling on.

focus on all +crit, +int, +con in that order. +spell damage has limited use when most of your DPS will be from instant spells. you shouldnt even need a tank or any more than your 3 mages once you get this tactic down.. mobs will only get a couple of swings on you before theyre nova'd and critted to death and you have 3 novas to keep mobs locked down while you CoC or spam arcane explosion. bind a key to "move backwards" on all toons so you can nova and step out of melee range if your previous nova breaks early.

same tactic should work in PvP, too.. except that youd make the decision whether to open with frost bolt from range (vs warriors, rogues, etc) or get in their face with frost crits if theyre ranged toons (casters, hunters, etc)

remember to precast shields before you engage, obviously.