How to temporarily disable the Finder application?

You should move away from force-quitting Finder.

Use graceful quitting:

    defaults write com.apple.finder QuitMenuItem -bool YES
    killall Finder

You now have a regular "Quit" command, not in the Apple menu but in the Finder application menu with corresponding keyboard shortcut cmd+q.
This makes the Desktop clutter disappear and Finder won't launch if clicking on the backround picture or the Trash.
This is a nice and easy option, and it should be enough!

Bonus: if you do this for 'enforcing more CLI usage/skills', then that means more keyboard centric activities? ➞ Turn on Dock hiding (System Preferences ➞ Dock ➞ Automatically hide and show the Dock). Then use cmd+Tab to switch between active applications. This further minimises chances for a 'mis-click' on the Finder icon that would cause an unwanted relaunch.

For the case presented as is in the question the above is quick & easy and a non-running Finder is reversed easily with one single click of the mouse (or for those wanting to improve their CLI skill with a open -a Findercommand in Terminal…)