I can only comment on BP tubs, but I move my babies from a V18 tub at about 500-600 grams, depending on how well they're feeding. Into my 28qt tubs. From there I basically eye ball it and if I feel like their too long for their current tub I move them up to a CB70 size tub.
If you aren't going to be breeding for a while, a sweater box (~28qt) size rack should be good. However if you're looking to breed, a CB 70 might be better.
I use mainly RBI racks and they're awesome. I have the V18 rack from CSerpents also and its awesome for housing hatchlings.