Pamda will have to answer the measurment question, but my guess is the size of standard stationary. You'll also be getting a "Get Lei'd" door Magnet, that Linda Griggs is making for everyone.
The cabin doors are metal, so magnets would work for holding decorations, little suction cups, or even plain old tape.
How carried away you get is up to you. Decorations can be garnish or garish <G>