Nice technique, I took the liberty of making a PDF of it.
Although I did not follow it exactly here is what I came up with using your brushes and Wilbur.
I think my main deviation was leaving the brush layers as normal and then I used the color picker to get a shade of gray to fill the land underneath all of the elevations. Then I fixed up the peak areas in wilbur with mounding [EDIT - I remembered I did not use mound in wilbur, I went back into GIMP and used Angular Fill on Blend tool for the peaks] and incise flow. Then erosion cycle on the whole land mass. Oh yeah and I did the original DEM in GIMP. I dont know about the layer style but you can run a palette map to see the elevations better.
And have some rep for the brushes and an interesting technique.