We have an LG fridge that uses a similar concept. It's shown here:
LGYou can open the right hand top door two ways. The first gives you access to the stuff you use a lot. Milk, butter, etc. The other way gives you access to the inner compartment you access less frequently.
Between these two compartments is clear plexiglass with a small cutout. The cutout allows cool air to get to the front compartment but isn't big enough to allow a lot of air to escape from the rear when the front is opened.
I don't think you'll need the insulation, just an air barrier between to the top and bottom. The top will be opened a relatively short time so the conduction losses will be small from bottom to top versus convection losses. Just stop the convection loss.