Any dumb eReaders? Kindle/Kobo/BOOX/Nook usability questions!

TL;DR: What I'm seeking:

1. wired transfer of books from iPad/iPhone or PC to the eReader

2. ePUB, PDF, and other format compatibility (or the ability to jailbreak and get compatibility)

3. dumb storage, the ability to use w/o ever connecting to wifi, no company having access to my library, pushing software updates, etc.

I've been wanting to buy an eReader for a while now but idk what to get. Essentially what I want (and I'm not totally sure it exists) is an almost totally dumb book storage device. I want to be able to turn it on and access my library, (no wifi) and I want to be able to send books from my iphone or PC to the eBook library with a wired connection without bringing it online anywhere. I'd like it to be just as close as possible to the concept of physical book ownership, and I don't want to find out that one day I can't use it without downloading "xyz" update from whoever sold me the device five years earlier.

I kind of feel like the kindle has the best hardware relative to the cost, but I hate the surveillance, data collection, etc. I've seen people recommend Kobo and BOOX but they're a lot more expensive. I can get a pretty top of the line used Kindle locally for like $50. I also currently have like 350 books on an ipad, would it be possible to buy a kindle, keep it offline and just move books from my ipad over to the kindle via a wired connection (formatting incompatibilities notwithstanding)? Does anyone know if it's possible to basically keep a kindle offline forever, away from updates and amazon eyes, and just use their nice hardware?

Is there an eReader out there that is capable of acting like a dumb device and just being a digital storage repository? I guess I'm wanting an eReader that is kind of like an external hard drive in terms of loading and storing books etc, but of course something I can carry around and read from.

Thanks in advance!