What level should I start Dawnguard?

How high level should I be before starting Dawnguard DLC in earnest, on a new character, to get a good experience out of it? Is there a lot of creature scaling in Dawnguard, fights or leveled loot that would be a lot better later on, etc? I never finished it years ago when I last played.

I’m on vanilla so I don’t want to wait too too long to stop the vampire attacks on towns.

With this character I’ll be on the anti-vampire side, if that makes a difference.