I have an Optiplex USFF and can confirm. If you don’t need like 2,5 Gbit Ethernet, ECC or other „server“ features they are a pretty good deal.

Yes. I didn’t have any problems so far. I guess, it’s because all my services are used by around four people, so the load is pretty low.

I am hosting both Forgejo and Immich in Docker Containers. I use the example docker compose files from both projects with minimal changes to fit my setup. The volumes are mapped to a Synology NAS that is connected via NFS to the Docker host. Backup is another synology NAS at my parents house. I never had to restore, so I don’t know how easy that would be…

Same for me. I use most of my services multiple times a week, so I find out pretty quickly if one isn’t working.