World population has more than doubled since 1974, so I bet the president can kill a whole lot more than 70 million people in 25 minutes nowadays. That's not great given how much stupider and crazier our current president is than even Nixon was.
Lol, a lot, but not that many. Mostly docker shit filling up /var from containers I'd tried running or run for a while and got bored of. Just needed a good docker prune -a --volumes.
Do some searches on "kiosk" software. That's the general term of art for machines that are intended to run a single program/interface. As for distros, you'll want something light and easy to maintain, ideally with automatic updates. Debian's an obvious pick. Alpine could be great for something like this. Gentoo could be awesome too, but there's a serious learning curve involved.
Did it currently have windows installed? If so, have you turned off secure boot and fastboot?
If you've done all that already, then maybe try adding nomodeset to the kernel parameters in grub. You can find instructions by searching how to set kernel parameters. It's fairly easy, but kind of a pain to explain.
To back it up I believe you'd just need to backup your .pass and .gnupg directories.
I haven't used keepass, but the entry from the archwiki should give you a good idea of usage, and it also lists some helper apps: https://wiki.archlinux.org/title/Pass
In the US, many public universities allow access to the public, including use of computer terminals that will allow access to paid databases. In many cases, you could bring in a usb stick and save copies of articles downloaded from such databases, or at worst you could pay a small fee to print some stuff out. AFAIK, that kind of access varies state by state though, so you need to call university libraries near you to find out.
You say this machine is headless. Is it at a remote location? If not, is it feasible to connect it to a monitor an keyboard for a few minutes? If so then you could logout, switch DE, and then log back in. That would hopefully set the DE you prefer as user default.
If that's not possible, then some of the solutions discussed here might be applicable.
I'm a college professor in the humanities (religious studies, history). Got into linux about 5 years back, partly because it comports better with my lefty politics than the alternatives, but also just because I've long been a closet computer nerd. I currently run a couple of proxmox servers on old optiplexes I grabbed off ebay. Full *arr stack with jellyfin on docker, a Tails VM for TOR stuff, NAS (omv on a vm), some other dockerized stuff: linkding, radicale, alexandrite (a self-hosted lemmy client, which I'm currently writing this on), various backup utilities.
It's basically just a hobby for me, though the switch to linux has also totally changed my academic workflow, e.g. I do all my writing in nvim + latex now, use syncthing to sync my home desktop, laptops, and office computer, etc. I dig divesting myself from corporate computing to the greatest extent possible, appreciate the privacy benefits, and generally just enjoy the community-driven spirit of the whole thing.
You can do all kinds of stuff with the config file. See here.