Who is Red John?
"He is a Man" - yes, he is a male.
"I only wonder why the two of you didn't become life-long friends the moment you shook hands." 
- Red John isn't Jane's friend, basically every male in the show is a suspect
Red John kills the most in Sacramento so he is a male living in Sacramento.
He is good with computers.
His methods of using people are similar to Brett Stiles.
He has connections in CBI, FBI so his job most likely is related to  Law enforcement institutions ( he can give you a new identity).
He must be very unnoticeable guy since no one can't notice him.
He likes Bach, literature, limousines (CBI and FBI like limousines a lot too).