Just fed on someone when I was stage 3. Am I stage 1 now?
Yes. You get the message: your vampire powers recede after you feed. This means you're back to stage 1. No more hostiles. Probably safe to become a werewolf now. If you actually want to become one. If you don't want to be either you need to do the vampire cure quest and tell the companions you don't accept the blood. You can remain human (or any base race) if you wish it.