Thestrad webpage focuses on supporting string players, with good resources on practice, technique, teaching music and collation of articles on repetitive practice and the need for effective practice. All in, a good resource of pragmatic responses to assist the learning of complex skills.
I had a look at other resources for learning music and came across some books including one on piano pedagogy.
At the CPIT library, there is a scholarly book on teaching piano – Teaching performance: a philosophy of piano pedagogy by Swinkin and published by Springer in 2015.
The book provides background (some historical) on approaches to teaching piano. The aims of the book are detailed in the introduction. Chiefly the book undertakes to try to resolve 2 dilemmas. One is to bring to the fore, the difficulty in studying music as language, the other is to push teaching of music beyond the technical, to instill greater intellectual depth, emotional sensitivity and interpretative skill in musicians. Unfortunately, I have yet to find an equivalent for trades pedagogy. So, there is a gap in the literature to be further investigated :)