I seed several thousand torrents that compose over 50 TB of content, and qBittorrent barely uses 1-2 gigs of RAM. It uses that little even though I set the max usage to 5gb. As far as the processor goes, that barely gets touched unless I’m doing maintenance and need to recheck the files, in which case my CPU usage hovers around 5% or less. Honestly, the thing that gets the most action from qBittorrent is simply the hard disk. I found the recheck goes faster if I set it to just one at a time so that the disk doesn’t bottleneck—the CPU and RAM will already be more than enough, even on a mid tier machine.
Now Plex on the other hand, that bad boy can max out a CPU like nobody’s business if the settings are right, but since upgrading to a Ryzen 9, even “make my CPU hurt” won’t take it above 80%.
So basically, the torrenting is pretty low footprint, but serving torrented content for streaming, especially when transcoding is involved, can be much more resource intensive.