Thanks for everyone's help, I think I've got a good grasp on the situation now, I'll go with the tank+3x shamans+1 approach.

One more question, how does tank+ 4x dps deal with healing? Do you assign one of the shamans to heal as needed or is there some system for this? I remember Heroics not being THAT easy to heal through when I last played, specially for newly dinged lvl80s.