Well… goodbye #UBOSlinux, nice idea, quagmire of an implementation and dearth of community, and 62 hours wasted.
Switched to #nextcloudpi and not only was it up and running in minutes, adding usb storage was trivial, can use the whole sdcard, and follows version updates. And it's Debian, not some custom fork of another o/s.
Although letsencrypt is not yet cooperating…