I'll make some guesses about who's who by generating ideas which solely binds me but maybe some people might agree...

Red John: Complicated. How? He seems to be a master-mind of crime as well as the cover-ups by highly smart moves that nobody could catch him so far. He is also a great manipulator/mentor who controls many people by means of persuasion? hypnosis? threat? blackmail? whatever you call it, people die for him intentionally. We see this pattern in some terrorist organizations but even in those, people may kill themselves under drugs mostly. However, RJ disciples reflect more of a sane pattern which makes us think that they are not drugged but they are somehow influenced. So, I am asking myself: How come such a crime-artist / well-organized brain can get so aggressive and stupid enough to kill people who just insult him? You don't expect such a temper from a man like this. It seems like an instant and not well-thought behavior which is almost amateur act to me. I can't just combine these 2 qualities (mastermind / jumperboy) together in one man. This is why I think there are 2 characters making the concept Red John a whole. There is one orchestrator and one killer (besides the accomplices). Perhaps the mastermind and psycho killer are having argumentations on each other's acts to eliminate contradictions. However, this only happens when there are serious contradictions. Otherwise, there's a master plan and they both pursue a unique goal by their own ways. For instance; maybe the mastermind got mad at the psycho about why he killed Jane's daughter where it was totally sufficient to kill his wife and let the girl wake up in a blood bath. And the psycho retorted that the girl got awake during her mother's killing so it was inevitable to silence her too. This kind of stuff I mean.

STILES: He has a bound with RJ as they were sharing a common context before things get ugly between them. They are both dangerous and equals by many aspects. So, they still have an understanding. RJ never intrudes Stiles' area except for some little touches (using Visualize resources from time to time), and in return, Stiles doesn't reveal who RJ is yet feels confident enough to share some little info with his rivals (Jane for instance). He actually told Jane that he knows everything about RJ but there is a certain limit to what he can reveal. Seeing this, I think it can be safe to say that Stiles has a history and an ultimate understanding/a silent agreement with RJ. Both being equally dangerous can be seen from the fact that Stiles is still alive despite he gave Jane an advantage at some point by letting him know where Frye was. Was it an order given by RJ? I don't think so. Will they be coming to a point where they have to fight? Maybe. Maybe the Visualize coup was a warning by RJ to Stiles telling him that he has to behave (against his revelation of Frye's location). See? No direct action but cold war between the two. Hostility and mutual respect is also there. And Stiles wouldn't show this courtesy to a simple psycho killer I believe. There must be a higher path.

I don't know if I should nominate certain characters who's the mastermind and who's the psycho killer. To be honest, I am guessing that the killer is Partridge but I haven't figured out who the mastermind is. Having Brett as the killer will make sense to most people which will also come with a great disappointment for the show but the show will pull it together with the reality that it's not over yet and that there's a bigger picture. That's where the excitement will arise again. This is what I think will happen. Enjoy it fellas... 

I believe it's Kirkland.

The on-screen handshake was visible, and slightly awkward.

His agents broke into Jane's "office" and photographed his research, allowing him to easily "predict" Jane's 7 final suspects.

He knows Jane was in a mental hospital.  During his stay, Jane likely told his doctors about his "happy memory", so all Kirkland had to do was request the doctor's files in the name of homeland security.

If I were Jane, I'd organize a meeting of the 7 of them at CBI HQ, and have the blind woman pop out of a door and identify Roy Tagliafero.

He is many. Specifically an organized group with one true killer/mastermind and dozens of other followers and pawns willing to kill and die for him. If red john has to be one of the 7 suspects I'll go with bertram; however, kirkland, stiles, partridge, haffner, and minelli are his friends and main accomplices. Here's the evidence:

1. The actor playing Bertram was born in 1962. He'd be 26-27 in 1988, the possible first Red john murder. Most serial killers commit their first murder at an average age of 25-27. The timeline fits perfectly. Could easily be involved with visualize and stiles and haffner at this point.

2. Bertram is manipulative and deals with media at the CBI. Note that red john is very concerned with his image in the media and how he's portrayed. Just like Bertram.

3. Bertram might fish with minelli and could have met Jason Lennon while fishing as well. Explains their friendship and connection. We also don't know about Bertram's past or life like we do the other agents at CBI.

4. Alexa Shultz worked with Bertram and seemed uncomfortable around him. Could be an act. She's also the one telling minelli about jane's stay at an insane asylum at the request of Kirkland. If minelli and Kirkland are working together and reporting to Bertram then they could easily track down Jane's therapist at the institution and hypnotize her to get Jane's memories, feelings, and mannerisms. This is how red john knows Jane's happy memories. He doesn't have special powers he's just messing with Jane and jabbing at his confidence.

5. Bertram was with Jane which is how he knew where to tell timothy carter to meet him at in the season 3 finale. Also Bertram disappeared after Jane went to confront him along with the red shirt guy. Another follower possibly.

6. When he kills he leaves no evidence. Is it because he's really good or because he has Brett partridge, who's always the first at the scene during red john crimes to come in and clean up making sure all evidence is gone by the time everybody else gets there. Remember partridge said he was working on red john murders since he started.

7. Lisbon's been acting weird lately. Like she's might be an accomplice. As a matter of fact ever since she started playing poker with Bertram and the others. You do the math. They've gotten close, Lisbon seemed worried Jane suspected bertram, and has been really prying at Jane trying to get any clues. Keep in mind red john seems to find out a lot of info about Jane's plan that only he and Lisbon were aware. I smell a rat.

This is my theory as how Bertram could be red john and how he'd pull it off with his accomplices. Let me know what you think.