Quantity   Component name
1 × Arduino Pro Mino
1 × Arduino Nano
1 × ESP8266 For prototyping I may use a Wemos D1 mini
1 × i2c LCD Screen 20x4 if it fits, or 16x2
10 × Buttons For D-pad, A, B, Start, Select and shoulder buttons
1 × Power circuit For handling 5v requirements, potential battery charger
1 × Game Boy Advance case Available on Ebay for a few quid
1 × Perfboard For fudging together all these connections and also for creating spacers for the buttons