OK so I want to overlay a series of images...

How do I do it in the darkroom? The negatives are all in the same lighting/setting so they would need the same exposure.

Do I just determine the exposure time for one negative and then divide that by the number of images that I want to overlay as a starting point? I'm not sure if I would be able to capture all of the mid tones.

If it matters, this is of a person flapping their arms trying to mimick the concept of motion. I would want atleast three negatives but hopefully more (maybe wishful thinking).