I also highly recommend libby, which lets you check out ebooks and audiobooks from your library. I don't have a kindle myself, but this help article says it's supported "Reading Kindle Books on a Kindle ereader"
You can also add multiple library cards, so if you wanted to go crazy you can find libraries that let you sign up for a card even if you don't have a local address and get access to both library's collections to read on your Kindle
The pinebook's privacy switches (for WiFi/BT, camera, and microphone) operate at the firmware level, the operating system has no control over them
https://wiki.pine64.org/wiki/Pinebook_Pro#Privacy_Switches