If you’re using Windows then Foobar 2000 is great. I use it for manually managing and tidying my collection in addition to converting pretty much any format to any other format.
That being said, you can install it as a snap in Linux as well if that’s your poison.
And shouldn’t be so tall that you need a winch to get over them without trashing the bottom of your car like the new ones near to where I live.
Also using Jellyfin and it’s great.
Regarding the number of different clients, yes they have less than Plex but remember Jellyfin is a free product and is a considerably younger project so more clients will come in time.
I run a Jellyfin add-on with my Kodi setup and it runs great and streams to three of my mother’s LG TVs, one uses a web client as the official client hadn’t been signed off by LG, another uses the official client (LG run multiple versions of their WebOS) and the third runs the official client on fire stick from the Amazon app store.
Absolutely second Unraid, easy to set up, Parity drive gives you protection against drive failure and dockers are an immense bonus. I have Jellyfish as a docker to serve my media around my home or when I’m out and about. Can use Gelli on Android just to listen to the music on my server.
Other plus, Unraid is essentially a JBOD so you can increase its size when ever you need to.
Think I paid £60-70 about 8-9 years ago and it’s been worth every penny.
Can’t praise it enough.
I usually scan my media with Media Elch before I move it into Kodi/Jellyfin then I know the files and folders have the right names and all Metadata is correct.
TV shows are grabbed, named and tidied with pyMedusa.
I use Kodi on a RaspberryPi with the Jellyfin add-on so if I watch something remotely then the watched status is synced everywhere.