I'd say definitely avoid a second pally whatever you do. During normal questing most of the time your healing pally would just be dead weight (melee dmg problems, nothing to heal, etc.)

I'd really be more inclined to say 2 shaman, both elemental for the first... 60 levels and then move one to resto if you wanted to be the holy trinity of a group. Otherwise just stay elemental and it's really easy to tank and DPS.