What are the specs and how are you finding the performance?

Maybe Pihole/Adguard home?

What else should I self-host, aside from HA (I don’t have a smart home), Calibre (physical books are my jam), and Jellyfin (I don’t watch too many movies + don’t have a significant DVD/Blu-ray collection)?

You sound kind of like me, but physical books are not my jam. I host a lot of things I use all the time. The most used app I selfhost is SearxNG. When you get it all set up, in your browser settings you can substitute DDG for your private SearxNG instance.

I host Obsidian which is a note taking app. It houses all my compose files, step by step tuts I've written to myself, interesting code snippets, etc. There are several encryption plugins for Obsidian that allow you to encrypt the document itself to keep it away from nosy people.

I host Readeck and Karakeep. These are bookmark type apps. I use Readeck for 'read it later' type articles I find are interesting. Karakeep I use for data preservation. Both can be used for both bookmarks and data preservation, I just keep 'em separated.

I host a lot more but that might get the juices flowing as it were.

I want to add dockge, for making it easy to manage / update your docker containers.

https://github.com/louislam/dockge

Love it. Saves me lots of time.