The bunk in a 4-person cabin is a couchette bunk, not a full-bed sleeper. This means that you will have a blanket and pillow, but you would not really be able to get fully undressed before going to sleep. The couchette accommodations are cheap and not uncomfortable, but can't compare to a real sleeper, which also has a washbasin in the compartment. For couchette passengers, washrooms and toilets are at the end of the car. On your train snacks and drinks can be obtained from the sleeper conductor, but only sleeper passengers (on some overnight trains) have breakfast included in the fare. Nevertheless you can get something to eat from the conductor, but since the train arrives shortly before 7 A.M., I would wait with breakfast until I could get a proper one in Duesseldorf station or in a cafe nearby.