I think the book you mean is "The Virtuoso Teacher"? I see a chart about simultaneous learning, but not a book titled that way. Either way, probably the book is a valuable read.
But, part of what sprouts the question is that I really don't know that there is a learning institution or curriculum or any type of program that would be right for me, to help me pull everything together that needs pulling together. I am wanting to pull together singing, composing, piano, pedagogy (especially towards piano and music in general), and those would include a deep(er) study in related subjects, too (and, ultimately, I'd like to pull a couple of other art forms and even science and spirituality all together). Is there really a place in the world that would be as interested in helping somebody like me pull such a big thing together, as much (or more?) than they are interested in simply letting a virtuoso instrumentalist or singer, or a designated composer, pass through their school and possibly into a designated profession? More and more, I am brinking on believing and feeling as though there is not such a place/program.
For me, I don't exactly know how to fit myself into what currently exists in the world, and all of those aspects that I mentioned above are already so tied together that it seems nearly impossible to decide something like "OK, I will "only" be an Opera singer", which has felt like some dilemma all along. I don't mean to and actually can't seem to exclude a portion of it all, because my greatest concept of music and living a musical life includes them all together - so, it has been my experience, that while I can focus on one at times more than another, ultimately I need them all in order to understand even a particular aspect by itself best.
And anytime I have questions like that about myself and the world, I think about it all as it relates to teaching and (possible) students, and what I can do as a teacher. But, since teaching is part of what I am still pulling together, that aspect of my musical concept affects my entire musical being, including my own playing. Do I sit at the piano and simultaneously madly keep a written journal with all of the thoughts and connections and concepts that are filling my head (almost beyond my control) while I am playing? Or, do I forget about trying to teach and trying to formalize musical connections between the elements I listed above for the moment, and rather "just sit there and play" while trusting the connections are formalizing themselves in a way that will become clear on their own, and that when they are clear, I can write them down at that point? I sometimes don't know which to be or do! And, then, that very quandary creates a problem that didn't exist before.