I haven't tested on ios for a few months, but my experience has been that the differences between ios and other platforms in the last 2 or 3 years have reduced considerably.
A while back I compiled a list of the included fonts for each platform (including ios). What are serif and sans serif fonts on different ebook reading systems?
When I test on ios, I don't sideload anymore. I found that uploading through the Kindle Manage your Content and Devices is sufficient.
The main issue I encountered with Kindle on ios is that your styles don't work on larger displays (and that affects image sizing and placement). For that reason you need to use css media queries to differentiate between display sizes. I wrote which breakpoints I used on this thread (ignore everything but the last Update section) https://ebooks.stackexchange.com/a/6027/417
Some advanced designers/testers will note more subtle differences in support, but generally if reference the font correctly, handle images ok and used css media queries and have good fallbacks, everything will be sweet.