Everyone knows almost all self help books are a bunch of BS and/or common sense ideas combined with encouragement and motivational techniques. I'm guessing most people who buy these kind of books don't do much research or read many reviews, but rather just walk into a bookstore or do a cursory search on Amazon or something and buy the one with the flashiest cover and biggest promises. There seems to be a built-in audience that swallows this up, especially in the colder months of the year when people get fat and depressed.

I don't really know how to write a self-help book in part because I've never really read one of those giant all-in-one tome style ones cover to cover, but since there isn't much substance if any to most of them, it seems like paraphrasing/rewriting an existing book with different language and some perfunctory reorganization should get me off the hook for plagiarism. Since I don't currently have a job but do have some available funds, I will be able to devote time to promoting the book and I'm sure I can put together a solid enough schtick to suck in all the gullible, desperate people looking for an excuse to spend money on something that promises to instantly turn their lives around.

So, is this a plausible idea? What sub-genres of self-help could be most suitable for this endeavor? The only one I can think of off the top of my head that probably won't work is a diet book because that requires some atual substance, and I'm looking for something that's mostly fluff that will be easy to copy without plagiarizing. What is a plausible range of how much money I could make doing this?

I'm not sure there's any money to be made rephrasing content alone, but if you coupled it with a speaking or consulting career, it could give you a massive boost, far more than it's worth.

That said, you need a speaking or consulting career to begin with, or new material for your book.

you also need a publisher

If you're a very good writer and charismatic, sure. Otherwise, no. You have to be the ideal, yourself. All self help book guru's appeal to the masses by being what the masses want to be, if not subconsciously.

Being a shameless hack is a talent in its own right. If you have that talent, go for it.

But actually the kind of people who are really successful at this stuff believe in their own shtick. You're too cynical, sorry.