Floyd R Turbo
Either busy or sleeping
The overall tank and sump will be around 65 gallons. Ill have around 5-8 fish in the tank and will be bare bottom. How large will I need to make this, or can it be a relatively small ats?
Relatively small. You are likely to feed in the range of 1-2 cubes/day, 2 being on the rather heavy side for that size tank. Generally I recommend a minimum size of 2 cubes/day, mainly because it is easier to light a 4x6 screen than a 3x4 screen, plus that gives you a little room for error - meaning, if your flow isn't quite right, screen is not rough enough, or your lighting isn't "ideal", your scrubber should still perform well enough.
Look at the posts in my signature for the latest basics. It's a few years old, but everything still applies, the only updates to it that are really needed cover LED lighting, which is also covered in this thread if you search my posts from the last few months or so.