You sound like you want to go all in on federated services but there are plenty of other things to do.
I love Nextcloud, works well when set up through the Nextcloud All In One docker setup, but it is a little different to other things so it might not be a starting point depending on your experience. Lots of apps to add for extra functionality. But don’t replace your cloud storage with it until you’re confident of your backups (and ability). I ran it for years to use for the apps and minor things before I finally went all in.
I think a wiki is a great thing to have. Use it to document what you’ve done so you can remember.
Then there’s media. With the storage I guess TV/movies might be out, but there’s Audiobookshelf for Audiobooks, Kavita or Calibre Web for eBooks. I like Jellyfin for music (but using the Finamp app not the Jellyfin one), but others like dedicated music setups like Navidrone.
I buy my music from Bandcamp where available and Qobuz where it’s mainstream labels, then I can have my own little Spotify. Finamp even lets you download playlists or your whole library to your device for offline listening. I use Findroid for watching things, which also allows downloading. Last I checked the Jellyfin app didn’t have Netflix-like downloading, just downloading the files to your downloads folder.
I guess you might not fit a whole lot with 300GB storage though, especially after you fit the databases of half a dozen federated services.
If you have space, perhaps a photo service like Immich or Photoprosm.
If you have friends maybe a private sharing forum like Zusam.
If you have family then maybe family tree software like webtrees.
I run so many things, they all get used, and I’m always happy to talk about them!




Even better than a coin flip is asking this what to do then doing the opposite!