I think this covers it. I went and read your requirements doc on Google, all of that stuff really reduces to one simple concept: you want a modern, dedicated e-ink reader with a screen of 8+ inches that supports epub. That rules out most of what's on the market and quickly narrows it down.

A mainstream somewhat affordable device that meets your spec is the Kobo Forma. There are similar sized devices running Android 6, but you've already said you don't want that, for instance you don't want it to have a web browser you want it to be dedicated. Since I've actually used the Forma hands on, I can recommend it. It handles everything I want quite well, including PDF's.

For PDF's, if you read a lot of them, as in every day, you are going to want a larger device for that, probably at least 10" is the consensus around here. In that case, what a lot of people do is get two devices: a separate, smaller ereader, and then a tablet say 10+" for reading PDF's, web browsing, media consumption.

The other alternative is a really large e-ink device up in the 10" range. Those don't come cheap, and the two options that come to mind are something from the Onyx Boox products, or Sony. I repeat--you aren't gonna like the prices.