Based on your description, it sounds like all of the paths you need might already be in the artwork.
You'd use a combination of; View / Outline Mode, Group Select Tool, and Cmd + 2 (Object / Lock / Selection) to find them.
Otherwise, here are the steps I used to reproduce your issue..
Do you know of a way that I can use the layer already created to make a mask? The above is useful in creating a new path, but doesn't really address my question on how to utilize that to mask the bottom layer.
The pathfinder can be used to combine and cut shapes out of each other. That being the case, you'd need to combine the white pieces into one combined path with the Unite option and then use the resulting shape to cut those parts out of a filled circle.