I think it's actually possible to win on the second guess with any initial input. Or at least I did it a handful of times..
It's not guaranteed you will always win in 2 steps because occasionally you will win in 1 step.
Yes. Yellow and grey mean exactly the same thing in this game: Flip it.
Hoping that you are being sarcastic...
This should be correct. For any cell that isn't green after your first guess, there's only one other possibility for its value.