Most juveniles will eat more feeders per day. I would recommend dusting with calcium one batch of feeders a day for 4 days of the week. Vitamin powder should be dusted for one meal. Until dragons are fully grown it's usually best to let them eat as much as they want. I always feed my babies in a separate bin; they each get a turn to eat as many as they want in about 5-7 minutes before I take them out. Very young babies get fed 2-3 times a day, Juvenile/Adolescent get 1-2 feedings a day (all they can eat in 5-7 minutes). And Adults over 18 months get significantly less protein (as they are done growing); they get 5-10 roaches 3 times a week. I have to add more feeders if the bin starts to run low. You don't want to put too many feeders in at a time or else the dragon can get overwhelmed or stressed out.
You should be supplementing both Calcium and Vitamins for the best health benefits. Most bearded dragon keepers swear by Rep-Cal supplements:
If you have a powerful UVB source such as a Mega-Ray you can use the calcium with no D3, but studies have shown that blood serum levels and bone scans are better if given both UVB and D3 oral supplement, I personally bought a tub of the D3 and non D3 and mixed them to cut the amount down since my dragon receives over 150uW/cm^2 of UVB from his Megaray. I've also rescued and recuperated several babies before and found new homes.