I messed up the bottom part of my original DMG so I ended up ordering a new one. The screen is GearBest which was rather easy to modify to work with 5v, sound is PWM with a low-pass filter and the L/R buttons are scavenged off a 3$ SNES controller. No USB hub, USB audio or teensy board, cartridge is only decorative.
Anyhow, after a several weeks of carefully poking at stuff this is what it finally came to be...
Shell replacement from https://www.banggood.com/Full-Housing-S ... 8146.html?
On/Off slide switch https://www.banggood.com/5pcs-6-Pins-Sl ... 3806.html?
3.5 inch TFT Display https://www.gearbest.com/development-bo ... 29447.html
micro USB https://www.gearbest.com/other-accessor ... 92914.html
DMG common ground PCB from ebay http://www.ebay.com/itm/Nintendo-Gamebo ... 615949649?
Screen lens from Deadpan Robot https://www.deadpanrobot.co.uk/game-boy ... -gs-blk3mm
PJ325 3.5mm audio jack https://www.aliexpress.com/item/10Pcs-P ... 56325.html
Power strip from OSH Park https://oshpark.com/shared_projects/tQqjx16m
Raspberry Pi zero W,
Powerboost 1000 C,
PAM8302A amp and
3.7v 3000 mAh LiPo battery from a local Adafruit seller
resistors, caps and wires were mostly scavenged from old electronics