Had a go using JoyToKey on a button box I had made (for flight/racing sims), using Leo Bodnar 32input interface:
I love it! I'm planning something similar but struggling to find throttle levers and stuff! Might power mine with an Arduino or Raspberry Pi
I also built a button box like yours, but I have run into some issues. Most notably, I have to press buttons for a long time before they are registered by the game. I have checked that this is not a problem caused by the joystick board/software by opening Notepad and pressing each button. Unsurprisingly, the key presses were registered immediately. This problem also occurs when using my regular keyboard. I am not experiencing these problems on TS20, so I guess it is something to do with how the game detects inputs from the keyboard.