To be perfectly honest i use 41qts for my snakes, no matter their size, and they do fine. I just built a rack and designed it for 41qts. It will hold 7 tubs. Its the perfect size for my room and will fit anysize bp basically. My juvenile cinny is only 300grams but he does fine in it. I have 3 hides in it and crumbled up newspaper and hes never missed a meal.
With that said once i have my own place and have more room (and more snakes lol) ill definetly have seperate appropriately sized racks for males and females. But for the time being i know i wont get more than 7 so it works perfectly for me.
I keep mine in a 2 foot by 2 foot cage from day one. as long as you give them good hides it shouldn't be an issue, but if you ever get one that won't eat, a smaller temporary cage/tub is a good idea to have on hand.