If you can figure out the impedance of the game-cube input,it would help,
I doubt it, all inputs on digital systems are high impedance and outputs low impedance that is how digital systems work.
Logic has what is know as a fan out, that is how many inputs an output can drive. This is typically about 20 so adding another input is not going to matter much.
though that is a good place to start)
No it is not.