Hello,
I would like to encourage you to ESP32 board, which has way better parameters than Arduino, has more builtin components (like WIFI, Bluetooth) is low-power and is cheaper.
And can be programmable in micropython (which I prefer, but I can quickly learn C++ programming in ESP32 or Arduino context).
Question #1 is - what kind of communication between device and game will be? Bluetooth? Wifi? Cable?
Question #2 is - if I'm awarded with project, will I get copy of your game to be able to test with? Will my duty be also make modification in game?
Question #3 - what is idea behind selenoid valve in game? Could you give some example of usage? Do you want game controller to flow REAL water during game?