sudomod

So I started building a GBZ in a GBA shell about a year or so ago and just came back to it but lost a lot of the info that I had written down about the project so am in need of some advice. I have the project to the point where the screen board is modded and functioning correctly on the lithium ion battery I have for the project and I can boot the system up into retro pi. the main facets I have to now work on are the audio system and the control system.
As to the advice that I would like, I realize that I will need a teensy or other similar microcontroller board but I'm not entirely sure on what the option are in terms of comptrollers that are suited for the purpose of converting button inputs to keyboard events. I'm also not exactly sure what the best option would be for amplifier circuits as I lost all my notes on the audio system I had planned. I would very much appreciate advice in these areas in order to push my project forward.

Here’s a Teensy LC on Adafruit: https://www.adafruit.com/product/2419.
I personally recommend a Pro Micro From Sparkfun: https://www.sparkfun.com/products/12640. Because Sota has excellent documentation and guides: viewtopic.php?t=1615. And it can have 14 buttons and 2 analog sticks. But for audio I hopefully this guide can help: https://sudomod.com/game-boy-zero-guide-part-5/. And here is the audio amp I recommend: https://www.adafruit.com/product/2130. And here is the speaker I recommend: https://www.adafruit.com/product/1890