In my Marauder era fic they're all about to get their O.W.L. results. I would appreciate some answers to these questions.

The people concerned are the four Marauders, Lily and Snape.
The subjects are, Transfig, Charms, Potions, DADA, Herbology, Care of Mag.Creatures, History of Magic, Arithmancy, Ancient Runes, Muggle studies, Divination and Astronomy.

1) Do you think any of these six took all 12 subjects?
I'm thinking that James, Sirius and certainly Snape had the brains but would they have bothered with some of the subjects? (Divination and Muggle Studies spring to mind.)

2) Which subjects do you see any of them getting 'Outstanding' in?

3) Can you see James, Sirius and Snape failing any subject they took?
I wondered if James might deliberately fail Divination or whether his pride would get in the way?

4)Is there a subject that you could see Peter getting a higher grade than his friends?

5) Out of the six people who do you think would have done the best?

6) Can anyone tell me what Arithmancy actually is?
Sorry that sounds like a frivolous question but I'm not sure what it is and need to decide if someone like James or Snape would have bothered with it.

7) This may be an error but Hermione got 10 O's and one E in her O.W.Ls. She'd dropped Muggle Studies and Divination so is there a 13th subject that I'm unaware of?

Please share any insights you may have.