Really interesting! Thanks!
Part of the reason I ask: I bought a Synology (4-bay, 1 TB each in Synology's RAID 5–like format) a while back with the intention of using it as a hybrid NAS & server. But have been repeatedly struggling to get it to do actually run the applications I wanted to run. And then started trying to get some of the things I wanted to run on my Synology to instead run on a Raspberry Pi...same problem. The weird architecture and distro makes some things not work smoothly. So have been thinking about getting a Mini PC with a standing x86_64 processor running a standard Linux distro to be a proper server, and using the Synology more exclusively for file storage & sharing.
Some of the things you listed there are definitely things that were on my radar to get around to running myself anyway (e.g. Immich, Watchtower). Others I had never heard of, but was already considering looking for an equivalent (Affine, Jotta—though for notesI was hoping Nextcloud would have a suitable app), and others I didn't even think of (Linkwarden looks very interesting).
Since you've got a Synology already, I'm curious what value you see in the Mini PC running a Samba server? I'm also curious why you go with the Synology as your reverse proxy. Just the ease of the included tool? Does it also handle TLS termination, or how does that work in your setup?