Spendy devices with amoled are only worth it for video or graphics applications, in my experience. I own and use both types of display.

For something that's primarily a reading device you can get by with LCD or e-ink. But if you can find an affordable device with amoled built in, it certainly isn't going to hurt anything, it's a nice extra. For size, there's pretty good consensus here on MR that you want around 10" or greater of screen to read full-size PDF files--I had a thread on this just recently. E-ink tablets at that size are incredibly expensive, and incredibly underpowered vs their Android counterparts. Thus, what you you need is simply a 10" Android tablet with sufficient DPI/PPI resolution (there ARE no good Windows tablets that fit these specs other than Surface Go, and trust me, it has issues of its own; and you said Ipad is not an option for you). Generally with larger devices, "good resolution" for reading IMHO requires at least 230 PPI; less than that, and you'll see distracting fuzziness around the font edges and other details. Of course 300 PPI and above is even better, but often this gets prohibitively expensive.

Knowing what OP is looking for, from specs listed here and conversation in other threads: best call is wait for the Samsung S5e tablet. It has everything you need, and will run in the $400 to $450 US range, which is pretty affordable for a tablet with those specs.

If you can find a Huawei Medipad M5 Pro (I see them on Amazon US for $450), that's an alternative worth considering. Although, with the S5e coming shortly and with better hardware, I think it's worth waiting for. ETA, FWIW, I'll be putting my $$$ where my mouth is: I plan to get a new S5e myself, to use primarily for larger document/PDF reading tasks, media consumption, and light productivity work. It'll make a nice complement to my S10 phone, which I am loving. It too has an amoled BTW, which is gorgeous and has an entirely gratuitous but still awesome 550 PPI. :-)