I only have ad-supported games in there, so I can't comment on taxes and other things.
I don't have a Kindle Fire - my games are exactly the same on Google Play. They have a test/approval process, just like Apple.
The Google statistics are way more informative than Amazon - Amazon only shows 'downloads' (in the report tool, they show downloaded/returned but that's it), not even active installs, which in my opnion is much more interesting to know.
That being said, my app was downloaded way more on Amazon than on Google Play.