I am very happy with my Pocketbook. Can easily install koreader (an ebook reader app) and connecting to a calibre server on my local network works very well.

I think the major ones are actually just android. If you were to jailbreak them I don't see why you couldn't just use any app then.

I use a kobo- has a blue light filter, waterproof, backlight. Not sure about the selfhosted library, I throw everything into memory which is enough for thousands of books.

Anything but amazon.

selfhosted ebook library

Is that what we call hard drives, now? :P

I have two android tablets, one 7" to read small books, and one 13" to read US Letter format books, I took the cheapest ones I found, disabled Google Play and installed F-Droid to install FOSS readers, and it just works perfectly. You really don't need anything specific to just read text, you just want to make sure that you can display an entire page on your screen in a size you're comfortable reading, otherwise PDFs becomes quickly insufferable.

Kobo Clara 2e