Keith, I am getting a lot of email from companies, like Book Avolare Book Discovery Program, The Book Walker, Writers Apex, Book Solutions, who want to rebrand my book
This webinar is all about Amazon Central.
https://www.authorlearningcenter.com/marketing/websites/w/optimization/8031/making-the-most-of-amazon-author-central
Here's a helpful article on how to recognize a scam
https://www.authorlearningcenter.com/publishing/preparation/w/choosing-a-path/7996/how-to-recognize-a-publishing-or-hollywood-scammer
And here's a book that can tell you about legit agents.
https://writersmarket.com/
Not sure where you heard that. I don't think chapter length matters as much as the number of total words in the book. And if the chapters are well written, readers will stay with it.
Glad they are helpful. Write on!