Is James Holmes the Joker?

Of course he is, at least in his mind, though there is a high degree of disagreement on whether or not he is insane... or not.  The important thing to not lose sight of in spite of everything is to try and understand what it is he thinks.  There is a lot of speculation what set him off.  It may have been something as innocuous as a traffic ticket, you have to remember that for how many years has he been told he is "special."  Imagine having a police officer not recognize that you are "special" and force you to pay a fine for speeding!  Jimmy Holmes was weak and did nothing, the Joker would have done something.  At what point did he begin writing the script he began playing out last Friday?  We may never know.
I do suspect the real targets were to have been the police and those victims in the theater were only the bait.  He was, after all, dressed for a fire fight with the police not an audience in a movie theater.  I think he also planned on winning that fight because the Joker would not be taken down.  Is apartment was rigged to take out even more officers.  Unfortunately for the Joker his gun jammed and he didn't have a spare.  I can not imagine what happened in his brain when the script he'd been writing and playing for months suddenly fell apart.  In Hollywood they edit and rewrite, he didn't have time.

I am the egg man, I am the Walrus, I am the Joker

Had his plan succeeded one can only wonder where he planned on going.  Does he have a hideaway somewhere, a lair from which he was planning on watching the chaos he had created.  Being as meticulous as he was, I would think so, and one can only wonder what horror he has hidden there.