I just switched from using Medusa and CouchPotato to Sonarr and Radarr. During the library import process, you can specify if the application should “monitor” the media which is what it means to download new content or try and replace with higher qualities. You can import entire libraries as “Unmonitored” so it will show it, but effectively ignore it unless you go back and change it. You can also just not import your library, and start “clean” if you wanted, and I believe it will just ignore the files for anything you don’t add.

I just checked on eBay, and there are multiple listings for single port 100 GbE Mellanox (now nVidia) Connect-X 4 cards in the $60-100 range.