Before I become committed, two things...
Firstly, I've only reached Season 6 Episode 12 (Still watching it) and I've done a little research. I want my character to be a vampire... possessed by a Demon. I've looked at research on Vessels, Demons, Vampires, and many other things... but nothing says a demon can or can not take a vampire as a host. I was hoping to do this, and also have the Vampires powers.

Secondly, if I recall correctly, we are at the part where Castiel brought Adam to Bobby's house and that's where Dean finds out Adam is Michael's new host... right? Because from what I remember, complete 100% that yes Adam is the new host is found out later, in another episode