My questions about the details of the partition were borne of the fact that nothing had worked for me so far, and were intended to ensure I hadn't overlooked something basic. Regarding the third question, it's still not clear to me how to use gparted to set a mount point (and I did look at the page you cited), but it doesn't matter anyway, as I used Storage Device Manager to accomplish that.
It may well be that I "don't know anything at all about something," but it was my impression that this particular forum was appropriate for beginners. Much about the Linux world is difficult to fathom for people getting started, and I've found forums more helpful than reference documentation for answering specific questions such as these.
In any event, I appreciate your initial helpfulness.
Pursuant to the original question, where it stands now is that backup returns a permission error on an attempt to create a directory, despite the fact that I've set the permissions on the new partition to full access for everyone.