With a fiber connection, 5-20 terabytes/month is nothing. I could probably ramp it up, but I'm only looking for 1080p content. The only thing that keeps me sub-petabyte is that my budget doesn't allow for a NAS with enough bays (and 20tb disks going up to $500ish here lately surely hasn't helped).
Really, just start downloading every new release and you wouldn't even have to dip into the back catalog much.