Looks great, Andrew.
Just a couple quick thoughts ...
Whatever footswitch you choose, you'll want to have 8 loop buttons, one for each loop on the GCX ... if you use a 5 button switch, two of them will have to be for "up" and "down" on the presets, which will only allow you to select three things at a time. In my setup, each effect is on its own loop (total of 7) and I use the 8th loop as a tap tempo for my delay. You want to be able, with one press, to switch in the Mutron, when you already have your delay, octave and overdrive on, for example (not that that would sound very good).
The Ground Control Pro has an advantage with the GCX because you can program everything right from it, save four instant presets for common settings, as well as switch the individual effects in and out of a given preset at a time, and plug in two expression pedals -- I use one for a MIDI rack wah in my setup, but you could use it to change the delay values on a rack delay, like Jerry did. The way my gear runs now, I have both the guitar cables running back to the rack, and the only thing running out to the floor in front of the vocal monitors is one MIDI cable for the Ground Control Pro.
I would tend to stay away from a smaller footswitch, although Rocktron makes a MIDI Mate ...
Also, make sure the footswitch can take its power over the MIDI cable from the GCX, avoids having a wallwart to go along with it and cleans up the cabling. Note that you'll need a MIDI cable with all the pins wired, some of the cheaper ones only wire 3 of the pins, so it won't deliver the power.
You definitely want a power conditioner, most people use a Furman. It will help you avoid current problems, as well as help with grounding issues. And, you can turn everything one with one flick of a switch instead of turning off all the rack units, the head, the power supply for the stomp boxes, etc. etc. etc.
I would guess that the volume knob was either an overall volume for Jerry's rig, so he didn't have to be messing with the preamp or poweramp settings on the fly, or it was a level for the keyboard monitor that was just to his left onstage.