If you work with a publishing services company, they will provide one for you. If you are using a DIY publishing path, you can contact Bowker
Glad they are helpful. Write on!
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.
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/
This webinar is all about Amazon Central.
https://www.authorlearningcenter.com/marketing/websites/w/optimization/8031/making-the-most-of-amazon-author-central