There are a number of areas in this project where multiple wires are bundled together. Specifically, connecting the control pad wrist board to the Arduino, connecting the Bluetooth module to the Arduino, and connecting the multiplexer outputs to the palm board. I found it useful to use ribbon cables for each of these connections. Here's a way to make ribbon cables out of old computer cables. Nobody uses floppy drives anymore, so they're a plentiful source to cannibalize from.
To make a custom ribbon cable, simply take a ribbon cable from an old floppy or CD drive, cut it to the proper length, and carefully use a razor blade to cut the proper number of wires from the original ribbon. These are a very nice, easy way to keep wires from getting tangled and confused inside the housings.