Reason why I'm thinking of 5 shammies is that I will have 5 at 60 anyway and leveling 5 should take around the same amount of time as leveling 4. Main reason for having 5 is that I already have a warrior and druid at 80, and I plan on transferring one of them to another account. I will then level a DK and paladin on seperate accounts as well.

That way I will be able to run my tank and 4 shammies from any account, but then eventually once they are geared up I will be able to try out my idea of 4 tanks and 1 shammie in the same group for heroic grinding.