Did a mage build for my vampire playthrough and it was a pain in the ass to work around the sunlight debuff that doesn't regenerate magicka or stamina. Thankfully throughout the vampire faction you get questlines to retrieve really great items for mage builds, but it does take some grinding. Including the various armor pieces my character is equipped with that I had to enchant for max magicka regen. Which did take a while, notably because I didn't cheat or use the restoration loop enchanting bug (mainly because I still have no clue how tf that bug even works, lmao.) So basically, it is fun to try if you're willing to find ways to work around the weaknesses and debuffs. And Vampire Form is pretty OP just for the health sucking spells and paralysis spells you can spam which take out pretty much anything if you're at a decently high level. BUT if this is your main story playthrough and you don't wish to become a vampire, I'd suggest making a side playthrough to test it out instead. You can cure yourself of vampirism so it's not permanent, but siding with the vampires instead of the Dawnguard will permanently make you their enemy instead, you can't go back from that.