Storing Bao Overnight--to steam and refrigerate?
As Jefromi mentioned in the comments, what you do is highly dependent on the recipe for the Bao you are making. Traditionally Bao is made with yeast but if your recipe includes baking powder as the main leavener, then you would need to steam the Bao as your recipe indicates. Otherwise the leavening will expend itself and you will get tough Bao.

If the Bao recipe you are using have yeast as the main leavening agent, then you can do either.

If you want to steam it the next day then you can leave the dough in the refrigerator to rise the first time overnight. You might want to decrease the amount of yeast used in your recipe in this case. The next day, take the dough out 2 hours before you want to steam it and let the dough sit for about 1 hr to get to room temperature. Then cut and form the dough into the Bao shapes and let it rise for another 45 minutes at room temperature. Then you can steam it. 

Resteaming Bao is not an issue if thats the route you want to go. A lot of places that sell Bao actually premakes it, steams it and then refrigerates the Bao. Then it is resteamed when it is needed. You can even freeze the Bao if you make a particularly large batch. The quality of the Bao won't degrade too much as long as you resteam the Bao.