I use Syncthing to sync the documents between my home server and all other devices. Additionally I use Obsidian as my interface (for this many other functions) but you could just access the files directly with a file explorer.

Same here. If anything I found Jellyfin far simpler to set up than Plex (used to use Plex, transitioned to Jellyfin).

I've been using Unified Remote to control my media PC (including any applications on it, such as Jellyfin) from my Android phone. I just use the track-pad remote, the keyboard input for typing, and the volume rocker for volume control. Though, there are lots of specialized remotes, including media remotes, available.

This has worked well on my media PC running Windows. However, I'm about to rebuild and I'd like to run Linux instead. In the past I've had trouble with Unified Remote on Linux; the text I type, especially when pasting, comes out as gibberish. As such I've been looking for an alternative and will probably give KDE Connect a try.