Tampermonkey by default doesn't have access to any files/data on your machine. Automatic updates and many more things can be configured in the settings (switch config mode to expert).
I still use XP SP2
If you don't like all these cloud and auto update services I recommend you to take a look at Linux Mint (I'm using the MATE Edition). Todays Linux versions are really easy to set up and they come with a desktop like on Windows as well.
Keep in mind that when you're working with such an old system, your whole pc is kind of a public cloud because it is attackable in more than thousand ways my friend ;)
Will give it a try, thanks - have already downloaded Mint, Sylvia Mate Desktop 18.3
:)