Start with the following plywood plate:
Connect the 12V power passthrough cable
Connect the 12V power from the XLR input
Connect the regulated 5V to the Arduino 5V/VCC pin
Connect XLR data in and GND to Arduino RX and GND pins
Connect the Arduino TX pin to XLR data out
Connect the 5V power wires for the LEDs to the buck converter
Connect the LED data wire to Arduino pin 2
Connect the three open cables from step 7 to the input of LED string accordingly