I will take a stab at a few. First off, I am mostly sure the Refer-a-friend thing doesn't work as well if a 70 invites, but I could be totally wrong. Amidst all of the posts I've read about RAF somewhere was something that you lack when you do this :/

I would say a paladin is totally worth it if you want to do PvE, and even in PvP.

If powerleveling is going well don't stop at 22. Go to 24 or 25. What I have noticed with my group (4 shammies 1 pally) is that the totem quests give a ton of xp and the shaman out pace my pally at times.

As for healing in PvP, yeah, that is a good idea actually. Once I hit 70 I will respec Holy so I can grind out a S2 weapon for my team. My paladin with heal primarily. Several people have commented that this works well, as I imagine it would.