Looks like a fun rack. I think I would want the sequencer in the lower left so that the knobs are unobstructed, and the output mixer in the bottom right. That way CV signal flow starts in the bottom left, goes up to the slew and VCOs, and then audio travels left to right and down to the phaser/delay and audio mixer. You could always add another VCO module, more envelopes, and some DC-coupled VCAs, but this would be a lot of fun as is if you want to keep it uniform. I don't have any suggestions for power aside from make sure you have some headroom. Good luck!
ModularGrid Rack