I can't answer all of your questions, but I can tell you that since this is an Android device, you can install most Android apps on it. Not all types of apps will work well, but you should be able to use pretty much any reader app you like (including Kindle or Kobo), comic viewers, epub readers, etc.
I think the MyDeepGuide videos on these will be very helpful to you:
Note Air 3 video review:
https://www.youtube.com/watch?v=HBHs1EPTUhE
Note Air 3C video review:
https://www.youtube.com/watch?v=8h_EZgusrP4
He really goes into a level of detail that you don't see much elsewhere.
Hope that helps!