The range of accommodation in Zhouzhuang is rather scarce. You will find some small hotels in the old town, close to the two main bridges. But you really do not need to sleep here. This is rather a daytrip destination.
From Shanghai, there are several buses every day. The first departs from Shanghai Bus Station at 7 am and the last at 10h55. You can get back to Shanghai from 14h30 to 17h30. I recommend taking one of the first buses to get to Zhouzhuang, and one of the latest to get back to Shanghai.