I was a long time Kodi user from back when it was called XBMC.
About 5 years ago I got tired of messing about with managing media, editing config files and installing addons. Moved to Emby first, and now I am on Jellyfin. No media management required, the backend server does it all for me and the front end is great, never gives me any problems and plays everything. I run the front end on multiple Nvidia Shields with no performance issues.
I’d manage your media better with movies and TV in separate parent folders and not all mixed together. When you setup Jellyfin, you point it at a folder and tell it what media type it is. Mixing up different media types in the same folder structure just makes things harder than they need to be for no gain.
No, Jellyfin has a server backend which manages the media and serves it up to the client frontends which support most modern operating systems like Windows, Linux and Android. See https://jellyfin.org/ for details.
I’d ditch the HTPC, and go for an Android based media player like the Shield, no moving parts, no keyboard/mouse and rarely requires an update. Had a HTPC for many years and anytime I wanted to watch something I had to mess about with it first before it would play.