Congrats!
If you manage to unlock Vampire, he's SERIOUSLY over-tuned at the moment. You should be able to beat Dragon Isles with him without any difficulty.
I wouldn't recommend using him for Naga City though. Not to say you can't beat it with him, but rather that doing so will prevent you from learning the dungeon. I've beaten Naga City with 7 classes, and 6 of them were using the same base strategy. Vampire was the 7th and played completely differently.