It depends on the size fish you want to keep and how many at a time you will have in QT. I would say a 20 long should suffice for anything in that 40 breeder. I wouldn't put anymore than 2 fish at any one time in a single QT tank, unless you are buying a school of fish or something.
I personally QT 2 fish at a time for my 90 DT. 1 fish in a 20 long and 1 fish in a 10 gallon. The larger of the two fish go in the 20, obviously.
For equipment, just put a couple of PVC pieces in the tank, keep it bare bottom, put a simple HOB filter, heater, and a cheap maxijet or bubbler.