I've used KDE on my convertible during uni and it worked pretty good. I mean for a GUI oriented setup your options are pretty much KDE, gnome, cinnamon, xfce (don't know how good that is with touch though) or cosmic (is that out yet? Idk tbh).
Afaik gnome and kde both have good touchscreen support, maybe you'll need to do some slight modifications, so I'd say just try them out and see what you like.
Afaik the X11 standard says that this shouldn't be done and that workspaces should span all monitors (or something along the lines of that), thus most DEs don't do this (I've read this in the gnome issue tracker), don't ask me why cause I also hate this behaviour. Most window managers will do that however and luckily it's super easy to replace xfwm with another window manager. I use i3 inside xfce on my work laptop, this guide describes how to set it up with ease
Alt/Ctrl+___ are usually used by applications and shortcuts containing Super+___ are usually "reserved" (it's no rule or anything but basically no application uses Super) for the DE. That's why Super is probably the best mod key for shortcuts. You can ofc use Alt+___ as well, in that case your DE/WM will just take preference over the application and the shortcut will be handled by the DE/WM instead of the application
I was lvl 100sth and on my Ng+ playthrough when learning this...
I've thought about trying that with my 7900xt, but never bothered actually doing it since everything I play runs on Linux. However I saw some posts about a project called something along the lines of pcie-passthrough-manager, that would be my starting point when trying that
My dad also made the switch to mint cinnamon about 3 years ago and I only had to fix things once for him (which was something in partitioning/fstab he or the installer messed up), he has successfully updated and maintained the system for 3 major releases yet and is even happier with Linux on his home laptop than with windows on his work laptop
Edit: he's not really tech savvy or something, he's a teacher by profession
But around the same time mozilla shortened the support cycles for their lts releases
There is a vim plugin called vimwiki which is pretty much what you're looking for I think, but if you're not using (neo)vim this won't make much sense I guess. Other than that I'd probably just set up a GitHub gist or repo with your doc stuff
If I'd buy a new laptop these days I'd go with a framework. Other than that, buying a refurbished ThinkPad is always a great option and they generally run really good with Linux. As for support I wouldn't be too afraid, almost all hardware is supported these days as long as it's not something really obscure. The main thing worth checking is probably the WiFi card, I heard there are some that are a pain to set up, but I never ran into that. That being said most manufacturers won't officially support Linux and if they do they'll only support fedora or Ubuntu (speaking about big manufacturers, ofc there's system76 and stuff), but as I said I don't think I've encountered a laptop that straight up wasn't able to run Linux. Also if possible avoid Nvidia GPUs, they work, but can be a pain with drivers breaking on the regular
I haven't read anything you wrote other than the title, but yes AMD is so much better, everything just works, nothing breaks with updates, no weird quirks,... It's just so much QoL you get by using AMD
Or embrace the hole and make it a perimeter
A friend of mine got his son to use Linux by just not providing an alternative, he installed Debian edu (don't know if that's the name, but basically a Debian spin for kids with parental restrictions and stuff) on an old laptop for him and that's what he used. Once he got his own PC it was over though since he wanted to play Fortnite so bad that he bought windows for that. He still dual boots Fedora, but I don't think he has used it since the windows partition is there.
I think the thing is you can't really get kids (or people in general for that matter) into Linux the way you are probably into it and interested in it. At least not if they're not already interested in it on their own. They will learn how to use it sure, but not the way we're used to using Linux, understanding the intricacies of the system, keeping the system safe,... They'll probably find a way to do what they already do on windows and ignore that the OS is different.