Guys, I'm SO CLOSE! Since the last update, i've glued the speakers and audio jack to the case and wired up the Teensy++ 2.0 to the Raspberry Pi. Another major change I made was to switch from my previous 64bit RetroPIe OS for the supported 32bit OS. I decided to switch to 32bit because I couldn't get the power button for the Raspberry Pi working properly. As soon as I made the switch, however, the power button worked great! And that's another thing i've added since the last update - the power button. I followed this tutorial on youtube to set it up and then wired the screen's power button the the same button as the one for the Pi, which allows me to turn both on and off at the same time. The only thing I'm waiting for is the heatsink for the Pi. I bought one that works great, but it's too tall, so I had to settle for this one from amazon. I'll update you when I get it!
There is one small problem with the power button that I may try and change soon. When I press the power button, the Pi powers down, but the red light and the fan on the heatsink both stay on, which makes it so the RetroPSU is never actually able to fully charge. This may be dangerous for the Pi and the RetroPSU, because I won't be able to tell when the battery is fully charged (because the green battery LED will never turn on while the Pi is still plugged in currently). I am trying to find a soulution to this and will update you when I find one.