Not sure about transmission but with qbittorrent you can go into settings and disable downloading of isos, exes and any extension and radarr and sonarr will never download those files. It will be a failed download and no mess to clean up.

Thats fine for an easy simple install where the work is done for you but it doesnt fully help understand how it all works. Its better to learn from scratch to understand structure and how each container interacts with each other, directories, etc