what you seem to look for is a book about psychoacoustics. but even on that level you'll just have to accept that for some unknown reason humans consider certain pitch ratios as pleasant and even those that sound unpleasant have their place to express dissonance and tension and it's culturally dependent also. eventually there will be first attempts at a general music theory of which the western key based frameworks are special cases.

Depends on your stats class. The one I took in college started from first principles, and was focused on proofs.