A full parts list is provided here, and thorough documentation of the power circuit is on GitHub. For a classic handheld take on the same concept, we featured two RetroPie Game Gear mods last year.
He’s using one of these to run RetroPie, which actually turned out to be much easier than installing a more general-purpose Linux distribution and then running various emulation software piecemeal.
Aesthetics, ease of use, performance, and supported systems - we've used several metrics to determine the best emulation platform for your tiny SBC ...