Personally, I would make all the walls the same height, and add a second ballast on them, especially the first and last wall. With the design you have currently, chaeto will break out of that clump and end up in the return pump are all the time, not to mention that when the pump is shut off and the sump fills, it'll float all over.
Beyond that I like the two live rock areas, and would return the skimmed water into the same chamber that the sump sits in. Without the double ballasts, you will likely have air bubble issues with your return pump.