You posted in the pvp forum, btw.

But I'll try to answer your questions.
For the Cataclysm instances, you need a dedicated healer, especially in heroics, so go Pally Tank, 3 ele, 1 resto. If you out level the normal instances, you can maybe get by with 4 ele. But Cata instances are considerably harder than WotLK instances were, especially the heroics.

If you're going to pvp in BGs, go 4 ele and the pally healing (or maybe ret). For Arenas, play just the 4 eles and get someone else to heal. You really can't box a healer in Arenas. I tried.