Depends on how many you want to keep. The larger they get, they more likely they are to start to prey upon smaller/weaker/molting siblings. Eventually, you'll have to separate them into small groups just due to size but I've kept whole broods in tanks that size and still ended up with 60+ crays (and then sold them, any larger -1.5"- and I would have had to start moving them apart).
If you're going to keep them in one enclosure, give them LOTS of cover (plants, caves, rocks, shells, etc ... any place they can hide from each other when molting, injured, smaller, etc) and keep them well fed.