You kind of have to figure that out as you get to know your FBTs. I know that if I put in a dozen or so crickets, Cortana and The Arbiter will eat about 4-5 yeah and Master Cheif is happy if he gets 1-3. You'll just have to see what happens. If you're getting your FBTs from different places or different tanks at the same place you'll want to quarantine them anyways before putting them together. This is a good time to figure out their eating habits.