This is one of those ideas that sounds great in principle, until you explore it a little deeper.
takes the best parts from each book and puts that info into his/her own words
There's the rub. His/her own words. That's your words. How good are your words? Unless you're going to fraudulently sell someone elses work as your own, you need to look at your own writing and communication ability. Are you clear? Are you entertaining? How well do you synthesise ideas from multiple sources? How well do you convey what you know? Furthermore, do you have mastery of the topic? It seems so simple to just "re-write", but if you don't have mastery of the topic, you can't tell the difference between a paraphrase and a misinterpretation. You don't know what's critical information and what's incidental. Oh, you can make guesses, but that's all they are: guesses.
This is an ethically dubious plan, but that doesn't really matter, because such a plan would almost certainly fail, especially in an already saturated market such as self-help.
Without compelling content, you're selling swampland. Don't become, in the beautiful words of Webwork,
the voice of a pretender to knowledge and experience.