the ONLY thing you got wrong is the excess of RAM, which is not possible to be used up unless youre running like 10 virtual computers inside your computer, which you dont have a reason to unless youre doing some hardcore testing/developing, or are making a server to run in the IT industry...

8 gigs, 4 gigs for the game youre running, the remainder for what ever background processes are running on your system thats it that is all you need not one gig more