Hey
I currently house 12 dart frogs

. Most of mine are juveniles (2-3") which I was told to feed 15-20 FF per day. As for my Azureus pair (3-4"), i feed them 25-35 FF per day.
Usually the fliers stay in the tank longer than the flightless flies because they hang out on the top of the tank where my frogs can't reach them. It's common for me to let some out when i drop in flightless flies. Possibly one or two at most; there aren't that many. ~A good way to trap them is to cut off the top of a soda bottle fill the bottle with a little soda, honey, few raisins, and a few drips of dish soap work nicely, and place the cut off top inside the bottom (top facing down) of the bottle without the cap, and it catches 90% of the fliers (which surprised me when i tried it).
I also judge feeding based on their size. If they look a little thin I might drop a few extra flies in the tank since my 20 gallon long tank holds four frogs, and my 55 gallon holds six. I just like to make sure they all get a good amount of food. If you have more than 5 flying or walking inside the tank, based on your viv size i might wait for them to get eaten first. 40 Flies in the 7 gallon viv might be too many to handle, and a slower constant feeding might be better for you.
My tanks also have established Springtail cultures and isopods cultures inside too.
Hopefully I'm not spoiling them. Haha
Hope this helps
dustin