Hey, I happen to like line art
but I also like shaded work. I used to do the light and dark on two layers like you mention but I kept forgetting to switch between them and got all fuddled. Now I mostly just do greyscale on one, if not the whole picture. And it is possible, at least in Photoshop, to separate individual values and colors to change them later if necessary, with a slightly more involved process, but I don't know about Krita. Anyway, as long as you don't forget which layer you're on, the method you're using is a good one and the result looks good. I bet a lot of people would find that tutorial useful if J. allows it, or if he posts it somewhere else.
Oh, and about the canyon... it looks good stylistically but you might consider letting it wander in direction more and add a few side passages that narrow and close off after a point.