Just a suggestion on the frame.... a butt joint (like you have where the vertical supports connect to the horizontal apron) isn't very strong, even with pocket screws. If you instead inset the leg (like is shown in Charlie's drawing) you can put screws through the legs into the apron, which makes a much stronger joint. If you need a flush surface for attaching plywood to, you can always just add filler strips to the front and/or side of the legs. I hope that makes sense. I can make a picture if it's helpful!