Please don’t enable this blindly. A lot of modern websites depend on a bunch of features which will simply not work with that flag enabled. Only do it, if you’re willing to compromise and debug things a bit

So that’s why we have mobile phones

Yeah, it seems like these immutable distros with individually contained apps (maybe with some additional restrictions and hardening) are similar to what OP wants. There’s a lot of distros like this

Nix doesn’t really guarantee reproduciblity, though. It’s a neat idea for deterministic configurations. But bit by bit reproducible binary builds are an entire difference beast. GNU Guix has way more promise in that regard

It’s console servers all the way down (up?)

Theoretically, yes. But I’m not sure if it’s gonna be smooth sailing. You would probably need a custom kernel which supports the kindle hardware. I don’t know if there is any project which already packages/distributes the kindle kernel

They come with a Linux based OS pre installed. Jailbreaking allows you to effectively become root and gives you a lot more freedom to change stuff.

TLDR: yes

That should alleviate problems with sending your mails and them not being in the recipient’s spam folder. The problem with less common tlds is that some ancient forms don’t validate them as actual domains. But this has improved vastly in the last few years. I would say just try it out, it should be fine.

It’s included