if the lab users aren’t adults; i would go with an immutable distro

It does not matter at all. All are linux. All work. It depends on what you do with it. There is no completely wrong decision.

Package update frequency:

With Ubuntu and with Debian there is also LTS (Long Term Support) to choose from. For Ubuntu this is five years for the default Ubuntu. I believe it is three years for the community flavors (Kubuntu, Xubuntu and so on). Personally I find the pushing of snaps and Ubuntu Pro by Ubuntu somewhat annoying and confusing, so I’d for Debian at your school.

Just wanted to say your English is wonderful.

I’d go with a stable distro, like Debian, or Mint if you wanted something that’s also rather stable and easier to use (Ubuntu underlying structure has a lot of fixes/changes compared to debian).

I think you are missing the most critical features, stability and support. You need whatever distro you pick to be solid. No one cares about the file system or whether it is immutable or not, your users need the computer to work when they use it, and nothing else matters.

You also need to be confident you can update and upgrade safely and easily, any risk of a broken update will make your life a misery when that happens.

Kickstart support, or some form of automated deployment will also be extremely valuable so that you can easily redeploy broken boxes with minimal effort. And some form of remote config/admin will also be extremely valuable. You dont want to have to do updates manually one at a time.

I would pick a general purpose commercially backed OS, so that if you need it later, you can pay for support if there is a problem. And you need to write some basic usage guides, because no matter which distro you pick, if its not Windows, your users will complain when they cant do X the same way it works on Windows.

1. C
2. B
3. A
4. B
5. A
6. A
7. A

Ubuntu LTS with gnome or linux mint. Most available documentation, easy to use, hackable if needed. Make sure it doesn’t crash on the kids!

I’d use fedora atomic, specifically ublue, because you can fully control what the os is.

1. It installs updates while it runs and at the next boot it boots into the updated image. If an update fails, it boots into the old image.
2. Most people don’t know WM. Use a DE. It doesn’t matter which one you use KDE or GNOME. Both are stable and solid. It’s up to you. Maybe choose it based on the apps you use.
3. Other questions are redundant.
4. https://universal-blue.org/ https://github.com/ublue-os if you’re interested, use https://blue-build.org/ and your own OS is ready to go within minutes.

Look at what schools in your area are using. Pick that.

If I had to make a recommendation outside that one: RHEL. You’re literally their target audience.