Hi

i would say it depends on your play style. Most 5-boxer are playing Tank + 4 shamans. I started like this too and now i play Paladin, 2 Elemental Shamans, 1 Balance Druid, 1 Holy Priest - and its fun to play.
u have many buffs and can handle nearly every type of debuff ( curse, magic, poison, etc.).

and with more shamans you have enough offheal in emergency situations =).

but as i said - it depends on your play style =)