Thank you all for your engagement in this topic.
So, please correct me if I'm wrong, the best way to have a reliable, error-free or self-error-correcting-by-LE system, will be to format the external USB HDD to one of linux partition formats (which one?), and then keep an extra laptop with a Linux distro, in case RPi fails, so I can plug the HDD to that laptop and copy necessary files, I may need, so I can use them under windows.