The "general rule" for cresties is 20 gallons for an adult, and 5 extra gallons for each extra adult. For a male plus a trio of females you're looking at about 35 gallons. The most important thing is hiding spots, though, so they can kind of get away from each other.

I don't have a rack system for my adults because I prefer natural set-ups, but some people use them. I do keep hatchlings and juvies in 12x6x4 inch ziploc boxes (76 oz). One juvie or two hatchlings per box. This way they are not competing for food, and I can see that everyone is still pooping.

In a larger container like a 20 gallon juvies can be housed together, but once they reach about 6 months they should be separated until they can be sexed. This is simply because breeding females before they weigh 30 grams can be detrimental to their health. If you're sure they are all female, though, they can just be moved to a larger enclosure together at that time.