I added 1/2 X 2 inch pieces of mdf trim to the bottom because the edges were so beat up.
Next, I filled the holes and gaps with wood filler.
I attached the new top using 1X8 pine and trimmed it down to size. Also, I attached 1X2 pine to the sides.
I did the same thing with the second level, and then attached the bottom with the original screws.