[Quoth]

Then it's an electronic version of a paper book. Not an ebook. Useless on virtually every ereader and needs 10" tablet or larger.

I made a mistake on the 70% option where Amazon takes 30%. It seems that's only a middle range of ebook pricing.
However more than $9.99 for eBooks is very rare, that's into paper pricing territory.

Your work sounds better suited to paper. Check out Lulu POD (Print on demand) as Amazon POD paper won't be stocked by some booksellers BECAUSE it's Amazon (formerly Createspace) and also Lulu has more options. It can still be sold via Amazon.

120Mbyte, 850 pages, fixed layout and loads of important pictures isn't a real ebook. Real ebooks are best suited to text with small images, line art, photo etc that are OK in only 16 shade monochrome. You need PDF for an electronic version and specify a minimum screen size and quality or else you will frustrate people.

Sell on paper and as colour PDF for 10" and better tablets. Forget real ebooks and ereaders for this book.

Almost no ereader of any format sensibly displays larger than a 6" monochrome page and many do fixed layout poorly, or only via PDF. Most Kindles can't accept Fixed layout Kindle format, that's for tablets and apps. Most non-kindle ereaders don't do epub3 (fixed layout), though many will do small page size PDFs.

No real ereader is better than 16 shade monochrome (white, black and 14 greys). Most are 6". More expensive ones are 7" or 8". Hardly any users have larger.

Colour and fixed layout only really works on 10" or better tablets using an app. Or obviously laptops/PCs.

Over 50% of ebooks are read on phones using an app.