lpi0 is limited by DRAM, and incompatible with Raspberry Pi's GPU, so we can't use RetroPie directly.
RetroPie is based on EmulationStation, and I have tried compile it for lpi0, but it have too much dependency to compile...
Then I tried mednafen, another lightweight emulator, it is easy to compile and works fine.
here is the link: https://mednafen.github.io/
joystick(wireless or I2C), speaker(1W or 3W) can be found in indiegogo suit, and lpi0-dock contains battery circuit too.