[Quoth]

Also unless you really really need epub3 (for a text book, video, fixed layout, interactive), use epub2. Gives perfect "Enhanced Typesetting" when uploaded to Amazon and they sell it as KFX. Also the regular azw for modern Kindles and apps will look the same as on an ePub app that honours CSS or an ePub ereader.

There are really four file kinds common on Kindle for ORDINARY eBooks:
azw = kF8 = azw3, can be basically an epub2 in Kindle format. User may have to select publisher option in Aa menu.
KFX. Usually the same content as in KF8, but the onscreen rendering is more complex (the advanced bit) and it's delivered differently to suit "Whispernet". Different DRM, even if publisher has requested no DRM.
old mobi. Older than Kindle Keyboard, plus the later DX and DXG. Less fancy typesetting etc.
Dual mobi. Not delivered by Amazon. Needed if you don't know what ereader someone has, it's old mobi and KF8 in one file.

There are other kinds of specialist mobi, azw3/KF8 and KFX, for things like dual format magazines, comics or fixed layout that's a little like PDF.

I have a Nook, three kinds of eink Kindle, Sony and Kobo eink ereaders as well as various apps on an Android phone and tablet to check that stuff actually works as intended. Once a set of styles is OK, I only proof on the Kobo Libra (annotate and copy back to laptop using Kobo Utilities in Calibre).