The *arr suite of apps is made to automate the whole process of building up your media library. You have Prowlarr for managing your download sites and clients, Sonarr/Radarr for TV shows/movies, Lidarr for music, Readarr for books, etc.

These apps can be self hosted and are fully open source. The basic workflow is that you add a movie/show, it automatically searches all of your download sites for the title, chooses the best download based on your filter criteria (resolution, size, etc.), sends it to your download client and then places the movie/show into your library based on the folder/file naming pattern you specified previously.

You can choose to automate as much of the process as you want or do most of it manually. E.g. grabbing new episodes as soon as they air vs supplying your own files (if you rip your media yourself for example) and only letting the program do the part of renaming and moving your files.