My hoodie uses 7 tactile switch buttons from this guide for controls. This is a good time to add buttons, if you desire. Then, come back here.
Once you've added all the LEDs you can handle, get out your JST on/off switch breakout board and your microcontroller. Set them in place on your hoodie, in the spot you chose in step 1. My switch is just below my right armpit next to the battery, and my Metro microcontroller is in the front right next to the closure.
Put the hoodie on and have someone help you feed the wires through to the right spots. The power wires from all LED strands go to the switch, and the data wires go to the microcontroller.
Determine the right wire length, then give yourself a couple more inches for extra slack. It's much easier to manage too-long wires than it is to deal with wires that are slightly too short.
Twist the power and ground wires coming from each LED strand together, add in one more wire to each bundle. This third wire will go to the microcontroller to give it power.
Solder the black wires to "G" and the red wires into "SW".
Sew the switch securely into the seam of your hoodie, and sew the wires down so there's no chance of them pulling out.
Connect Vin and G on the Metro to one of the wires from the switch.
Connect the data wires from the hood and tail neopixel strands to pins 8 and 9. Connect power and ground wires from each strand to the switch.
Connect the data wire for the button neopixels to pin 0. Connect power and ground wires to the switch.
Connect each button's green wire to pins 1-7.
Add tiny zip ties or sew the wires down to the hoodie for strain relief wherever you feel a tug as you move the hoodie around.