A chinese ootheca will produce upwards of 300 nymphs overnite! And each one of them will become quite a cannibal! You will need to decide how many nymphs you want to raise. The rest will need to find new homes. You can keep them together in a tank, but they will start to eat each other very quickly! Also, this species gets very big. The adult females will push close to 5 inches in length at times. So each will eventually need a 2 gallon tank if you want them to have some room.
I have to agree with robo mantis. I can not recommend the European mantids at this time. My first European ootheca started to hatch out a week ago. Half of the nymphs died while emerging from the ooth. The other half refused to eat. Out of about 100 nymphs, I lost all but 3!! Those 3 still have not eaten and so I doubt they will be around much longer!