Hi Keith,
I use yWriter to write my novels (currently working on my 3rd), which I, too, publish via KDP. There are instructions on the KDP site for formatting your manuscript using MS Word, as well as suggested fonts to use (Times New Roman is a no-go) and font sizes to use. It also has a table to work out the margins you need to set base on the page count for your manuscript.
For my next novel, I'm no longer using MS Word to format my manuscript but Adobe FrameMaker - I write training manuals for a living and is well-familiar with it, so find it far more powerful to use to format my manuscript than what you can easily achieve in MS Word.
My process when I formatted my manuscripts using MS Word looked like this:
1. Write the novel using yWriter (I don't include the front page details, etc. in yWriter - just the chapters.)
2. Export the yWriter Project to RTF.
3. Open the RTF file in MS Word and save it as an MS Word document.
4. I have a VB Macro that I run on the MS Word document, which applies an MS Word Template that contains the required page size, Paragraph Styles for formatting the text. The macro also updates of a couple of things, e.g. Chapter Titles, scene separators, etc.
5. As my novels are fiction, there's no TOC.
6. Make any manual tweaks to the document as needed.
7. Add the frontmatter and backmatter pages.
8. Save/Print the file to PDF.
I'm happy for you to contact me directly to give you some specific pointers. I'm also happy to share my MS template with you, if it will help.
Regards,
Quintin