Warrior + Priest + Mage = Possible?

I want to try multiboxing and I was wondering if this combination was possible. I'm primarily interested in playing ONLY in instances, as it's easier, has good loot, and I just hate running around the world looking for things during questing. I was thinking if I could quest till like level 15 on all 3 chars and then go to deadmines and grind it till I'm high enough to go to the next instance and then do the same thing there?

The way I figured it'd work is that I will control warrior as a main character who will do most of the work holding the mobs. I will then allocate like 3-4 keys for the mage and priest, where priest will heal whoever I select with warrior (thru /assist), and mage will AOE blizzard or nuke whoever I select with warrior (again thru /assist). They will all be on autofollow and stand next to the warrior at all times, so blizzard spam will hit everything.

Possible? Efficient? Comments? Suggestions?

There are no impossible combinations in multiboxing. Some have more strengths than others. It's really easy to figure out, too. Just take a random PUG of decent players with the specs you're thinking of, then consider how that group would do in the role you'd like them to play. The rest is just extrapolation and creative use of macros and keybinds.

As I get more and more spells, I am finding it more of a challenge to macro up stuff across 5 different classes, fun mind, not impossible by any means however it’s hard when you have more choice. Like tonight I found than the Shaman getting new healing rank at 18 has all of a sudden made him a bit of an aggro puller from my Pally, all be it I am not a great tank yet so probably more my lack of skills than the Shaman aggro however none the less I had to adapt and adapt I did simply by down ranking his heal back to the one before this, and that solved my little issue.

I do have 3 level 70s a Mage, Shaman and Priest (not mulit-boxed).. so as you can see I was never a tank but the main challenge of multi-boxing multi-classes has to be the macro skills and for me. I tried to keep it simple putting all long attack cast spells on same button, all instant casts and dots on same button, all heals on same button.. and of course have the tank as my main one I control, using healbot to monitor the others and I just click on who needs a heal then press my healing button and all healing class heal that person.. all simplistic but down the line I hope to get better at it all.