Its even better with a Kobo, because you can set it up as a Sync server and “replace the Kobo Store” with your Calibre server. It makes it so any book you have on your server will appear like something youve purchased from the Kobo Store, and let you download it from the server to device, directly from your Kobo
Not really - It depends on how you prefer the form factor. I liked the side handle of the kindle oasis, so I went with a Libra 2 during their holiday sales last year. If you like the normal form factor, then the Clara 2e/Nia is probably what you want (or an older model).
You can’t sideload audiobooks, so don’t use that as a deciding feature of which one you pick up.