To kill tanks more easily, shoot them in the turret. It seems the turret is less armored than the tank's body.
At the beginning of chapter 12 if you look at the right and the left there are buildings. You can go inside them. There will be machine guns too. On the left building the Nazis might throw grenades so be careful.
Hold Select and press Right, Right, Left, Left, Square, Square at the chapter selection screen to unlock all chapters and bonus content.