"It may well be that the most surprised person about his success in this campaign happens to be The Donald himself..."
I really believe this, too. I'm certain that Trump entered this thing almost on a lark, with no intention of getting too far. It would explain his lack of preparedness on many of the issues. But then it took off, and I'm sure he was surprised and said: "Well, looky what happened here!"
I don't think so. He's done this before, so sort of knew the ropes, and knew he screwed up by working through a minor political party. He's been asked about running for decades. If this was a lark, why use the GOP/RNC machine?
He has also consistently talked about the incompetence and corruption in politics.
He was in it to win it, this time.
I think he's surprised by many things on the way, including the sudden drop out of Cruz, who had appeared to be determined to stay in until the convention.
A couple years ago the GOP approached Trump abut running for Governor of NY. Trump turned them down saying he was going to make a real run at the presidency. He's been prepping since Romney screwed it up.