How do I assign multiple popups to a single button?
A button can trigger as many popups as you like, provided they all match the button name followed by the "-popup" hint.
Thus the button created from a layer named "Gallery-button" containing five layers each named "Gallery-popup" will show all five when it is rolled over.
Another technique is to place multiple layers in a layer set and name the set to match the button followed by the "-popup" hint.