What is the correct algorithm for reinstalling Mac OS X from scratch?

Question

Backup

My system has migrated from one laptop to another several times using standard system tools.
Once, it seems, unfolded clean from the backup.
Judging by the speed of work, it seems to me that it is time to reinstall it from scratch.
At the moment I do a full backup to an external hard drive and then upgrade to Catalina.
If the update is successful, I will make another backup and proceed with a clean reinstallation.
And here I don’t know at all how to do it right, starting with the issue of formatting the disk and ending with restoring application data, but so that the garbage is not collected back. I don't have many applications.
Applications
My questions are:
1. Is it technically possible to deploy MacOS from a backup in a virtual machine, in case you need to transfer something like custom hotkeys?
2. Is it possible to take partial application data from the backup?
3. If I upgrade my system to Catalina, does that mean I'll get Catalina on a clean install?
4. Pros-cons-pitfalls are welcome.

Answer 1

1. It is enough to copy the user profile folder, shortcuts are stored there. You can also find the file.
2. It is possible, but not the fact that it will work. Depends on the application.
3. Command+R: Installs the most recent operating system that was installed on your Mac
Option+Command+R: Upgrades macOS to the most current, compatible version
Shift+Option+Command+R: Installs the operating system that came with your Mac (or the version closest to it that's still available).
4. Everything is as always. Either install from scratch, or 10.15.1 is better to wait.