This is truly a great effort. At the same time I am frustrated by the choice of the medium. We are well past the age of disseminating information through print. I would love to "hear" the concepts described. Why not make an interactive web page? Maybe sprinkle some audio samples here and there? It seems convoluted to not use sense of hearing to describe music.
Indeed. The ability to click on an interval and immediately hear it -- and/or simultaneously see it played on the piano -- would be quite nice. (Or, conversely, the ability to see piano notes instantly rendered on a staff and have the intervals identified.) Combining two learning pathways -- visual and aural = win.
http://www.emusictheory.com/interact.html
and here http://www.emusictheory.com/practice.html
I largely ran out of time to extend/improve it several years back, but it still gets quite a lot of use; students of subscribing teachers can use MIDI keyboards as well, which makes the instrument/theory link quite tangible.