Serana wants to make me a vamo or trap my soul to get into the Soul cairn.
I'm already a Wolf, so can i become one after?
Also, if the turns me, does it make me a VL or just a regular vamp?
Choose the soul trap, you'll regret choosing the Vamp option. Trust me. You can get your soul back and re-visit. If you choose to become a Vamp, you'll only be able to enter the Cairn as a Vampire, and never as a normal human.
Also, she makes you a VL.