Wow. I’ve only just started testing it against GP, but it’s really slick and works really well. Lots more fine control than GP, and the only thing that isn’t quite as good is the photo editing on the app and web site, and that is on the roadmap. Oh, and I can’t see how to set up TLS but I might just be missing something.
Yes, looks like a reverse proxy is the way to go.
Immich is easy to handle with standard proxy settings, nothing special. My caddy entry for immich is the typical one liner from caddy.