Don’t throw away your Kindle, Jailbreak it and take back ownership. Make your Kindle even better with KoReader and other apps. If you wanna see whats possible i recomment this Yt video. If you wanna get started here are all instructions: https://kindlemodding.org/ Don’t let it scare you it seems complicated but its just a lot of (easy) steps. So definitely possible in <2h.
No but makes it easier to sideload and prevents amazon from owning/changing/deleting “your” books
You can still sideload afaik. You send the epub to the Kindle email. That still works.
My kindle hasn’t been online since 2012. Just buy DRM free books or pirate them, and then transfer via cable. None of the firmware upgrades introduced anything useful.