Question 1: Why would McCain bother with faking cancer if he could just shoot himself, if he was comitting suicide?
Question 2: You realize this isn't evidence, right? This is speculation. Nothing more. Trust me, it's good to be skeptical of what you see and to double and triple check your facts. But this is completely unfounded. I still see no reason to believe this. Provide hard evidence across more than 1 credible source, and then we can actually go somewhere with this speculation. Trust me, if you can give me a reason to believe there's something behind this, I'm all ears. But right now, it just seems like the president is listening to the words of a fringe conspiracy group that's gaining momentum quickly, and that even they aren't able to fully back up these claims.
Question 3 and 4, but I'll answer these: Is all of this possible? Yes, yes it is. Is it likely? Not even remotely.