I have some questions about completing the game and obtaining the S card.

I have just retrieved wendell and have a couple of things I'm unsure about completing the game.

1-How do you obtain an S card 2-How do you see what rating you are currently at 3-If you complete the game (storywise) can you go back 4-If you complete the game can you alter your rating 5-If you forget to scan a boss/one time enemy does it become impossible to obtain an S card

Would be greatly appreciated if someone could help.