Thanks for all the great feedback.
I decided to backup my SP4 to a 128 GB 3.0 USB flash drive ($25) and transfer it to an external HD. I used Paragon Backup & Recovery 14 Free.
The process was easier than I thought it would be. The PB&R 14 user interface takes some effort to figure out, but once you do, it's very simple to use. Also, incremental backups are easy to do and take up relatively little space.
My SP4 hard drive is about 45 GB (about half of that is music files, IIRC) which compressed to a 34 GB backup folder. It copied to the 128 GB 3.0 flash drive in about 34 minutes. I then plugged the flash drive into my desktop and copied the folder to my 4TB external HD in about 5 minutes. Based on my experience, incremental backups should only take about 5 to 10 minutes. Unfortunately, I can't automate/schedule incremental backups (like I do with my desktop) because my SP4 is turned off when not in use.