If it works for you and the data is not mission-critical, I don't see the reason to stop using it. From my experience, the much older and lower-cap drives tend to last really long. I still had quite a few Hitachi (now HGST) drives that are still running after 12+ years in my storage rack (on ZFS), which just refuse to retire to this day. Some I just need to retire due to their limited storage capacity.
32G should be plenty for such a use case.
Never tried that myself. I prefer to keep my drive "warm" 24/7 and "ZFS paranoia" during storage.
Portable/External HDD tends to die/silent corrupt without much warning. I will suggest that a proper 3-2-1 backup strategy is still preferred if you have the resources to do so, and the data is of paramount importance to you.
The rule of thumb is that "SMART" tests are deceiving and cannot be fully trusted. Same as you cannot just rely on the patients (storage drives) to tell you how they are feeling without the doctor testing out the symptoms. Truth is, conventional RAID (1, 2, 4, 5, 6, etc) is also not sufficiently competent to protect your data if you look deeper.