I want to make use of an enchanted item that you get from the VL side on a non vampire character, can I cure it right after i become on and still do the quests?

I would assume so, but I don't really know

Yes you can, but can you honestly justify doing the questline just for the ring of the beast or erudite? +100 health or magicka? You can get rings of peerless health/magicka that give you +70.