I think the real question is not "Who is Red John". If we know who is RJ, then there are other question will show that we have to ask. 

1) First of all, why RJ kills? Just an ego? I think it can't be. He has a powerful friends. If he kills just a reason of ego, why they support him? He must be good offer.

2) What is the offer? What can you offer to FBI agent, Homeland Security... Who really are you RJ?

3) This is a really interesting question that i wanted to know. His servants... Why his servants kills them selves? Think about it, look our world. Doing that thing people are usually do for a  faith, opinion, religion. RJ should give them a faith. Visualize can do that. We clearly see that. And i think there must be connection.

4) This question like the first one(just more ideas, short questions). For what reason he kills? Why a powerful man kills random, normal people. (I accept they are random, because if not PJ should have noticed that)

*These questions are relevant. But i wanted to ask in different numbers, because of little details.

When i analysed that questions... First i thought Bret Stiles can be RJ. Because he can manipulate, he can gives faith(at the cost of death). But he is not a potencially killer. But includes some of RJ characteristics. 

Bret Partridge has a killer characteristics. PJ finds him creepy. And he really is too. He can do RJ murders. But he is not a powerful man(we can see).** If he is powerful and he hides, why? I think there is not a logical answer. If we accept he is not a normal killer.

But if we combine Bret Stiles and Brett Partridge(names are the same is that a coincidence?) we can clearly see the Red John characteristics that we need. 

RJ has a connections, visualize too. But a powerful organisation(***) acts serial killer actions? Come on. This is the real question. RJ is powerful man. And if you want to use agents, you should give them a good damn reason. What is that reason? Why he kills? Why smiling face? We makes theories but no one explains included that questions. There is a good questions but we make it relevant and put it on a logic.

*** I used organisation because he has a powerful friends, connections. That makes you have organisation at least.