The goal was simple: a box in the closet that stores photos and backups, makes no noise, and does not need me to log in every week.
A fanless mini PC with a low-power CPU, 16 GB of RAM and two SATA disks in a USB enclosure would have been enough. I went with a small case that fits two 3.5" drives instead, mostly so I would stop worrying about the enclosure.
Plain Debian, ZFS mirror for the data disks, and a few containers. Snapshots run nightly and are pruned automatically:
zfs snapshot -r tank@$(date +%F)
zfs list -t snapshot -o name -s creation | head -n -30 | xargs -r -n1 zfs destroyOffsite copies go out once a week. Updates are unattended for security fixes only; everything else waits for a rainy Sunday.
Run a dozen services "because I can". Every service is something that can break at 2 a.m. Today the box runs four, and I could name each one without looking.