I've thought of writing several books. Your details are run of the mill. I feel for an editor to be interested you have to sex it up. Come up with a core thesis in two or three sentences and have everything relate to that thesis. Sex it up with gripping personal details. I was near death for decades with facial pain. A book could really sell. It would not sell if I said I had an illness, went to a hospital, etc. Boring. I would have to reveal soul wretching moments, intimate moments that reflect my thesis. This is why I write no book yet.
It is much easier to self pubish with the Internet. Certainly, preparing a manuscript might be cathartic whether it is published or not. I read a lot of nonfiction and hate it sometimes. Nonfiction works when there is a theme and a convincing personal presentation that is well written.
So many times I read nonfiction and become enraged that I am wasting my time and that I could do far better.
Frankly, no one cares about JWs besides JWs. People might care about dangerous cults if details are vivid and compelling.
Then again, I do read a lot of books that have been published that I hate.
Networking helps. Luck helps. There used to be a writer's resource sold in the NYC subways and major newsstands. It must be available online now.
Getting in touch with publishing houses to find out their concerns and processes would be a good start.
Ray Franz book was nonfiction and about a group I left decades before. Nevertheless, I could not put it down. It was a page turner and rivetting.