What are your experiences with self-teaching music theory? You don’t have to be a 100% autodidact to answer this question; you probably have had times when you read a book or watched a video to learn some specific idea or technique. Ideally, I’d like to compile some guides for readers who don’t have a teacher.
Personally, I prefer close reading of books and articles, but I know that’s hardly a universal approach.
Reger’s book is interesting because it doesn’t teach directly what it seems to be about (practical and musical ways to actually pull off these transitions) but it does teach principles of the fastest route and common tones to get your brain moving. Particularly C to B# major. You learn these 2 chord motions and how to daisy chain them.