[Ali-B]

sorry, back to your original question ( :p )
I have kodi installed on a fire TV, but unless you jailbreak it (or whatever the fire equivalent is...) you have to install it via the backdoor (ADB - a developer tool to sideload non-appstore apps) and even then, it's not available through the normal apps menu, you have to go through several system menus to get to it, so i'd stick with a standard android device, unless you don't mind jailbreaking the fire stick (not even sure what the current state is of that...)
my plugin of choice used to be genesis, but development of that ground to a halt, but i now use exodus which is more or less identical. (I'm not going to detail what it does but it's pretty much all i use in kodi now...)

Oh and a Pi 3 is overkill. a cheap Pi2 is fine for almost everything (I still haven't got round to updating off my Pi 1 B+ as it still serves me just fine despite having a Pi2 waiting in the wings )