2 is the max. like many already said, though I would always recommend maintaining one role-play character to avoid watering both down.

 

As for demons, don't get into it too much. After plenty of experience with players trying to act it out, and what we envisioned the lore to be, the limitations on demonic characters is intentional to avoid people from creating a lot of schizophrenic unrealistic demon characters that can just switch in and out of possession states whenever it is convenient for them in role-play.