You don't have to repeat the same element over and over again.
The idea is to use the style of the artist and improvise with this style and elements.
Think about this project as if you were this famous artist and you were commissioned to decorate a train car. You'll have to use the same painting style ( colors, brush strokes, elements from the paintings, etc...) to implement the rhythm concept. Remember - the car itself already has the repeating elements: doors, windows, spaces between the windows...)
You can fill in the area between the windows/doors or use just them, or use both... It's totally up to you.