Ok I nearly reached a decision on the setup.

I will do either a pally and 4 elemental shammy
or
priest and 4 locks


My two questions are:

1. How do you control 2 different classes (considering pally as main or priest as main). I think you need to micro manage the aggro on the pally to keep it high while someone also making the shammys do DPS

2. Which is a better setup for instances, leveling and evetually pvp (5 man)