Twister is finally all wired up! And it works! There are still some kinks to work out, however:

• I didn't realize that Arduino doesn't have a separate serial for the USB, and so the first MIDI port and the USB can't be used at the same time.
• One MIDI Input port of the 4 seems non-operational.
• A row of buttons wasn't working. I tested the board and the connections seemed fine, but soldered an extra wire to double that connection and it now works. Go figure.
• The headphone jack turns out to be mono, and so I will have to wait to wire it up until I have the right connector.
• The pin headers add a LOT to the height of the Arduino + Shield assembly, the wires even moreso, and it will no longer fit behind the display. The USB and power connectors will have to be relocated if they are to be accessible.
• The USB port on the Arduino Mega 2560 rubs up against the bottom of the shield board.
• The A/D lines are supposed to be 10 bit precision, but the value seems to waver by +/- 4, and so really there is only barely 8 bits of precision on them. My grand idea of sending sysex with greater precision values seems less possible now. 8 bits is more than the 7 that MIDI can send in a CC message, but only slightly.
• I forgot to make a mounting hole for the screen contrast adjustment potentiometer.
• Crimping pin connectors sucks. I never want to do that again.

Still, it works. I'll definitely work to get the mounting ironed out and write the software to run it now. I'll probably want to iterate on the design tho. Too bad I've still got 4 of these printed circuit boards left.