1. No controller support, sorry, I'm too lazy. V for night vision on keyboard.
2. E to open doors on keyboard. Says so in the intro video as "Interact". Sorry if that was confusing. Also, there are some enemies indoors, so it is required to go inside.
3. The gun has a suppressor, that's why it sounds like that. Personally I think it's pretty clear, but sorry if it wasn't for you.
4. Just press "Play" in the menu to start, like most games.