Has anyone does this yet. I most likely wont do this as my character still upholds Kodlak's teachings but I was wondering if you can become a VL or just as regular vampire if Serana changes you after completing the MQ.

You can ask Serana whenever you want to after the main quest, as long as you have not cured her.

Wait, you can cure her? I was curious about this cause whenever I bring it up to her she tells me to drop the subject.

Don't bring it up til end of main quest.

I've done it. The dawnguard shuns you and they won't talk to you until you get cured.