Well, I can't say that I've watched all episodes, but I'm quite certain that Red John is not just a single person, but a cult. Their members are all over the FBI and CBI, which is how "he" gets to know everything, or they are CEOs or such, which is how he funds himself if required.
I think Bret Stiles is definitely involved: Bret has shook Patrick's hand, their characters are similar - they both know how to manipulate people and they both are 'mentalists' (if that's the true saying) -. And he knows about Red John's actions. For example, he told Patrick the location of Kristina Fry.
Please leave a comment below, I want to know if I missed evidence or haven't seen one.