If you really want something upgradeable, used enterprise SFF is the way to go: https://discountelectronics.com/
However, the hardware market is in a weird spot right now; you’ll get far more bang for your buck with an Intel N150. You can find a 16GB DDR5 w/ 1 TB SSD around the $200 mark, and that’s what I’d roll with in your shoes, assuming you don’t mind living without a spinning disk. Your Jellyfin and Immich instances will run far smoother.
You’ll get used to it eventually, but you can e.g. tweak your PS1 to an all-caps hostname, or use a custom tmux layout with dedicated panes for each box you connect to.