Can I leave the rolled (unfilled) cake in the fridge overnight and unroll and fill it the next day?

You can leave it until the next day, but I would suggest leaving it at room temp. At refrigeration temperature, starch molecules begin to break down and shed their water, such that baked goods actually stale faster under refrigeration than at room temperature. If you refrigerate your rolled, unfilled cake, there is a good chance it will crack and break the when you unroll it the next day.