Linux

Have you looked at Mate Desktop? It's based off of an earlier version of Gnome but I find it much more familiar to the way things used to be managed on Windows.

That's going to come down to the specific hardware. A lot of vendors build their devices to only work under Windows but there are a lot of smart Linux techs who have been able to reverse-engineer working drives. Your best bet is to find a hardware compatibility list and see how much support your particular laptop has.

If you look at Debian, you can get the "net-install" image. This doesn't even install a desktop environment, it simply boots you to a command line and you can install whatever you want to use. Many other distributions probably have a similar installed available, it's just a matter of deciphering what the names mean.

If you install something as root, or if it's installed by the system during the initial installation, then yes you'll need root, but more likely you will use "sudo" which gives your user account the temporary access needed (if it was set up with that access). Again, going back to something like Debian's net-install, everything except the core OS would be installed by you anyway.

"Rooting" sounds like a term you brought from an Android phone. In desktop terms, think of the root user as being like the admin on Windows. You only use it when needed, like when you're performing a system update, otherwise you do everything under your regular user account.

When you install a DE like Gnome, it also adds a login to your graphical interface. If you install a second DE, then on the login screen you are presented a choice as to which one you want to use this time. If you want to switch, you just log out and select another one from the login screen. You can have as many as you want, just remember that this loads a ton of extra stuff on your system. It's ok to play with, but then I would suggest uninstalling the ones you don't like.

Wayland is the core of the DE. The previous system was Xorg, but both are still in common use. Docker is a container system, so like if you wanted to install a web server then Docker would contain all of the modules for that software independently of anything else you have installed. This means that a system update is less likely to break something (although that's already pretty unlikely), but it does require more storage space.