I would say no to both questions. The spell has a height of up to 30 feet above the floor it is cast-upon, that is what I would use for covering multiple floors with one spell. It would also be very confusing, for the following reasons:
1.) How does it interact with magic negation, such as Dispel Magic? If I successfully Dispelled one non-contiguous area covered by the spell, would I Dispel the entire area affected by that casting, or just the area targeted? The former seems like it would make the endeavor meaningless, since the villain would get better protection from multiple castings. If I could only Dispel the area targeted, then what prevents the villain from putting 480,000x 1 sq. in. squares with only 1/2 inches between the individual squares? Would I have to run-around casting Dispel Magic 480,000 times?
2.) How would this interact with casting and components? The spell has a static casting time which does not change with the area covered. Allowing non-contiguous areas to be covered would increase the area that can be effectively covered while having the same casting time. So, to cover 480,000x 1 sq. in. squares would have the same time and component costs as to cover 1x 40,000 sq. ft. square.
3.) What if one of the areas moves? What if I target a pallet or stone block that is being used as a floor, and then that block or pallet gets moved? Does the spell move with it? Or does it stay there? If it stays, does it remain in the same area and height where it was cast, or does it move to the closest "floor" space below the area that the pallet or stone block once occupied?
I would rule that, for every single casting of Forbiddance, you can create one area, which can be up to 40,000 sq. ft. by 30 feet. Multiple, non-contiguous areas would require separate castings of the spell.