I'm hosting Photoprism, now. But man, do I just barely use it. I'm not a photographer, and I always have the worst camera of anyone around me, so I'm never taking pictures. It's running, and I'm not taking it down. But it did teach me to use docker compose. I switched everything I had after that.
Matrix was one that was hard to justify. It was just too heavy. My dream has always been "use one app for all communication". I bridged Signal, Discord, and Facebook. Problem number 1 was that SMS is like impossible to set up. Problem 2 no one uses Signal except me and my wife. Problem 3 was that my Facebook got flagged for suspicious activity, and they wanted my ID to recover it. I used this as a chance to ditch Facebook, but I also ditched Matrix at this time. Signal supports SMS, so I could do more with it than Matrix. I'll probably try again down the line.
My most used service is definitely my music service, Navidrome. You might try it, it's very light. I used to keep all my files on my phone like you. And my phone had an SD slot, so storage wasn't an issue. But I couldn't listen from any of my computers, or at work. After I made the switch, I painstakingly re-'aquired' all of my music in FLAC, and have my phone set with a size limit of music to cache, as well as always downloading my favorites.
My first server was a Lenovo Thinkpad T420. It was given to me for free from my job. It did great. Built in screen, mouse/keyboard, and a built in UPS. Eventually I upgraded my server, and my new one has none of those.