My party generally consisted of Main (Mage), Leliana, Wynne, and Alistair. Wynne's a great healer, and my Main was also a Spirit Healer, so the team was never short on health. This worked well enough for a while until my main also specialized as an Arcane Warrior - I never saw a game over screen again.

Rogues are good for the chest-opening thing, aside from backstabs, trapping, etc. There's not very much that's useful in chests, but you can make a good deal of money selling any loot. Also, just opening chests by itself probably doubles the parties XP in any given dungeon. Rogues are necessary for that reason alone.