Excellent work! Couple of suggestions to make it more compact: 1) you could arrange the four buttons in a 2x2 matrix rather than vertically in a row, 2) mount the encoder thru-hole with a small daughterboard for the connections underneath, which would bring the height of the encoder down. If you make the 8-channels on their own module, and the master fader part of the right-hand side control section, then it would be viable to get PCBs made as a front panels and have the same 8-fader module as an expander.
