I quite like your design, especially trying to keep the number of rollers to a minimum, and keeeping them in an almost straight line.
Do I understand it correctly, that the dancer is used to both measure and control the tension?
So at times, the film would pass through 2 additional rollers (which on your not-to-scale model seem quite small, I imagine they will be as large as the others?) Wouldn’t it put less strain on the film if you’d replace the two rollers with just one roller that could push the film, and thus increase or decrease the tension?