You can try to plan accordingly based on the repoductive rate: you'll have to ultimately make the calculations because it all depends on approximately how many you feed on a daily basis.
You can expect a single female Blaptica dubia to produce about 20 offspring per month, I like to have 2-3 reproducing adult females for every nymph that I feed off on a daily basis. This allows you to hold back a few nymphs each month that the female produces to replace retired breeders or adults that pass on. You ideally want to keep a ratio of approximately 1 adult male to 3 females.
From your 400 adult females, your looking at a production of approximately 250 nymphs per day. You want to always set aside a few to keep the colony going as well. If you feed more than this on a daily basis, you should consider increasing the size of your colony to let it become well established. You can never have too many roaches; it's when you don't have enough that you run into trouble = )
Also, for best reproductive success: Keep them warm, have a good quality high protein diet available at all times (preferably very fine), and a water source/fresh veggies available. Try to keep them dark and refrain from disturbing them as much as possible. I'd suggest having at least two different bins for the size colony you will be maintaining - 1 for the adult breeders and one for rearing nymphs into feeders. It's easy to separate the baby nymphs from the adults periodically to add them to the feeder colony.
I remember the days when I was ordering thousands of crickets online weekly - them smelled, the chirped, they were dirty, and they are escape artists. Roaches Rock = ) And in the long run they are much cheaper and wayyyy less hassle amonst the points that were already made.
