Nice guide, but one thing that seems slightly off: All the cubes don't look exactly cube shaped, they need to be slightly taller to look perfectly cube. If for instance a cube is 2x16 px wide, then the height at the side should be approximately 18 px.
One reason is, at least, that because pixel art "isometric" is actually 2:1 dimetric, the vertical axis is slightly less foreshortened than the two horizontal axes.
Let's look at top surface. To have it 2 times wider horizontally than vertically in projection camera angle must be 30 deg down from horizon.
Ratio between the foreshortened diagonal of top surface and foreshortened height of the cube would be sin(30)/cos(30) if they were same length in 3d.
Since they don't have the same length in 3d (diagonal is sqrt(2) times longer than cube height) the final ratio in projection between cube height and diagonal comes out to be cos(30)/(sin(30)*sqrt(2)) so more than 19px and less than 20px (a little bit closer to 20px) for the foreshortened diagonal of 16px.
