I think that the doctrine "do, and understand" applies particularly well to classical music theory and composition, though I'm very biased in that regard. My post above mostly concerns the "theory of harmony", and my recommended way of learning that is to grab a textbook on the subject (one with exercises) and do the composition exercises. No need to play any instrument, as a geek you can use any software that features a good pianoroll. And here's the most opinionated part: teacher useful but not strictly necessary.