Deciding on your team is one of the toughest decisions you can make. It really depends on what your goals are for the team, too. If you want a PVE team, the typical group would have a paladin tank, a healer (strongly recommend priest due to the AOR healing strength of glyphed holy nova) and 3 DPS. If you are scared to make the mixed DPS different classes, it's not THAT hard to macro different classes up. I mean as a simple example, a warlock could cast shadowbolt when the shaman casts lightning bolt. But this community always strongly recommends shaman teams when you're in doubt, since they can all heal DPS and take more beating on than a normal caster.