I don't need a massive amount of text per spread. I am typically writing 200-300 words of general text on each spread and then the rest is explanation and teaching points attached to specific sketches. That's why the sketch-selection is so important.
I don't have to start from the beginning and work my way through chronologically as, for the most part, sections stand alone. My editor explained that, for this kind of publication, people rarely read from start to finish anyway: they tend to dip in and out all over the place. She suggested I begin where I feel most confident.
By the way, if you missed the beginning of this project and want to follow the progress of this book from the start, just use the Sketching People label on the right hand panel and scroll down. There have been 10 posts so far.