Around 2-3. Auratus can be breed in groups with positive results. What morph are you looking to work with? Each morph tends to have their own size. I know that the Panamanian Bronze morph is larger in size than the Panamanian spotted morph.
Any that you buy that are CB auratus. They make great starting frogs. Were are you located? I personally like the Panama Bronze auratus. Once adult size they will eat small crickets. That makes it a little easier to deal with just in case your friut fly cultures take a down turn.