Thanks for the replies guys.

I've played the games many, many times before generally focusing on just leveling 1 character at a time (I have dual boxed before but that was a priest/lock with the priest just following casting renew/pws/swp)

The main reason me and a friend are playing this time round is just to do 5 man instances. He's decided to jump on board so he'll be dual boxing and i'll be triboxing and the challenge is too see how far we can go (with MoP 5 man heroics being the highest we'll likely go)

I'm not very interested in raiding this time round (spent far too much time on it in the past and not too interested this time round), as for PVP we'll likely jump in some bg's but nothing too serious.

As for the class combination, what would you guys say the difficulty is between having multiples of the same class (ie 3 elemental shamans) as opposed to multiclass combinations (ie a resto shaman, feral druid and DK)?

I want a good balance between being able to min/max in order to do harder content (heroics) and simplicity.