I do have some food items from City Park Cafe that i can put inside, but as you can't really see them where they are displayed, I generally don't bother.
regarding the upper floors, I have designed an interior for the first floor in LDD, but have not built it, nor have I designed an interior for the top floor. This is because it is alot harder to see from outside the model, unlike the ground floor (without an interior, the baseplate stands out from a mile away...)