I am planning on a 5x druid team and here's what I was planning on doing.

1x Feral Druid, 3x Balance Druid, 1x Resto Druid

I figured then I could at least have a balanced group for PVE and could easily respec the feral to balance to tear it up on the BGs. Moonkin aura is awesome so you should definitely keep at least one in that form. Also, if they're healing, doesn't it just make sense to make one Resto? They definitely heal better than a Boomkin and you can leave the others in that form. Just my two cents. Good luck with your team.