I thought this would be fixed by the big machine they're going to use for the real test. Like, maybe it doesn't matter to the general population how much more powerful someone is above "base" S-class, but people who are S-class know approximately how powerful they are compared to each other?
It depends on what kind of software you usually use. You should look up the programs you use regularly/can't live without to see if they have Linux versions or if they have decent replacements. If everything there checks out, find an LTS distro. Debian/Ubuntu and derivatives (PopOS or Mint) or fedora and derivatives (I don't know any fedora derivatives) would be good.
I started using PopOS last year for a gaming machine and all the tinkering I did, I did because I'm a nerd and I wanted to. If I wanted an easy experience without even looking at a command line I think I could've.
One more thing. Most (maybe all?) Linux distros can be booted and viewed in a live environment from a USB without having to erase your whole drive (just make sure you don't go through the setup and actually erase your drive (unless you want to))
This might make me sound like a chess elitist, but it can't have been much of a chess club if they couldn't beat you because they "can't figure out what your next move is."
I know Samsung and pixel both have this option, and I would be surprised if other major manufacturers didn't. While people have their grievances with them, I've never heard anyone complain about overall battery lifetime.
If that is an actual concern people have then they can just turn it off by default
Any Debian/Ubuntu or fedora based distro will do you fine. I personally ran PopOS when I built my computer earlier this year and didn't have any issues with it
I set mine up with duckdns and caddy. In duckdns set the ip address to your machines local address. If memory serves, there's a section in the vaultwarden wiki about using caddy with duckdns
Oof ow my bones ouch