WC is cancer and I would avoid it. At 20 I would go run SFK. Much better drops, but be aware of the spell immune/silence mobs.

I leveled with arcane/frost shatter. Rotation was

1. Pull mobs
2. Frost nova
3. FlameStrike
4. Frost nova (not always needed)
5. Cone of cold
7. Arcane Explosion

Also, priest holy nova is, IMO, the MVP of AOE for multiboxing.

Note I did level with WMMMP. At 60 I find arcane/fire is much better. If I was leveling again I would probably go arcane/fire, filling in fire first of course.