Yes
There are some very old and quite rare books with lists and descriptions of some bit not all of the known demons. Barring that, research, research, research.in my experience please read psycology who belive in demons sure he have psycology problems god made that world savety.
yes
demonologist
Yes but be warned demons are unpredictable
Demonologist: noun:Someone who studies demons and beliefs about demons.Exorcist: noun:A person who is believed to be able to cast out the devil or other demons.
All demons are equally dark if you believe in such things.
Demons are typically portrayed as entities that hunt souls or prey on individuals who have vulnerabilities or weaknesses that can be exploited. They may use manipulation, fear, temptation, or deception to lure and ensnare their victims. In various mythologies and beliefs, demons are said to target those who are spiritually weak or have negative energy, often appearing when summoned or invited through rituals or occult practices.
Lesser Demons, Greater Demons and Quest Demons.
You need to do some research - writers do a lot of that! - and learn all about different types of demons so you can figure out a way to do that on your own. Using someone else's ideas will leave you at risk for getting sued if you sell the story and start making money. HERE is a link to a question about writers and story ideas, too.
There are thousands of movies with demons a few are the obvious Demons,Demons 2,Night of the Demons which has just ben remade any exorcism movies will have demons in them as possesion is a demon trick.
No they are not demons!____________________________________________________________lol -they are not demons!- though some of them look like it. . .
A paleontologist.