I agree with your first paragraph.
Not sure about the second. The guy's got more money than he's got a use for, and could make it faster NOT being POTUS. I mean, once you can afford one aircraft carrier, what's the point of a second?
I believe POTUS simply served one of two goals. The first would be ego. The second would be that he loves this country and wants to give back (though I tend to disagree on many of his methods).
I have a confession to make. I posted that because it was outrageous but wanted to provoke thought.
I do think that ego is involved. I also believe that Trump has used the inflated tactics mentioned in the book to gain his following. In other words the talk has been tough but the action isn't. He has built on the fantasy of bringing illegal immigration to a halt. It won't.
It was absolutely known that the Trump properties are built with illegal immigrants. He can say he doesn't hire them because the contractors do. But he never voiced any concern about illegal immigrants being used in his constructions.
As for business advantage. Of course in his business he will gain. When he goes back to private life his business, and the business of his kids will have benefited greatly. The only thing that I posted I don't believe is that he did it purely for his business. The only thing we really have to work on is his previous interviews about government and his thoughts on politics to work with. I remember a lot of condemnation on Iraq war but I don't remember America First.