I kept all of my Dubia together at first, but as I had more and more adults develop, I've started a second bin just for the breeders.
My main reasoning is that there is no need to sort through the adults every time I feed out of the nymph bin. This avoids disturbing the breeders unnecessarily and it makes it that much easier for me to grab the 50-60 nymphs I need at the moment for feeders.
It also simplifies feeding the roaches, because the adults do not consume food as quickly as the nymphs, which will eat a whole orange overnight and most of their roach chow. By feeding the adults separately, I can keep the proper portions in front of them 24/7, especially the oranges and other fruit, and the more voracious nymphs don't clean it up before they can get to it.
I go through the adult bin every two weeks, do a little refuse removal, cleaning and harvesting. I pick the adults off the egg flats and lay them back in the bin, and then shake the babies off the flats into the feeder bin. As I feed from the feeder bin, some nymphs will have reached maturity every day or three, and I just drop them into the adult bin to join the other breeders.