Hard drive allocation

Installed Fedora KDE along with kdenlive on my pc.

Currently have 3 drives, 1 with the OS and programs, 1 blank SSD that I plan to use as the cache drive, and 1 HDD for storing the videos I’ll be working on.

Is there an optimal location for which drive the backups and proxy’s should go to?

When I was adding drives to my PC, I had another spot available for a 2.5” inch SSD but didn’t have a data cable. If the backups and proxy’s are better off on another drive I can always buy a cable to attach another drive