The foam goes from the top and stops 3" from the bottom. This means the floor area is not compromised at all. The substrate goes up to the bottom of the foam.
I think the important thing is to give the frog some cover to hide under and feel safe. So a low level, broad leaved plant or a cave/shelter is all that is required for the frog.
You would need another tank for your frog for at least two weeks after using silicon as the smell is strong. The elaborate background however is not needed to keep a healthy pacman, but it does look great and is a focal point.