Perhaps history over media studies, but as youre already taking biology chemistry and maths, it might not matter as much? Media studies is sometimes considered a soft subject (not that this matters too much)
Won't matter. The only medical school that cares what even your thrid subject is, much less your fourth (assuming you take bio/chem) is Cambridge. All other medical schools don't care what the other subject(s) are. Also taking 4 A-levels confers no advantage in medicine admissions.
Take 3 - because taking 4 wont get you any extra credit, and you could mess up the other grades as a result. AAA will always look better than ABBB.
As above, for Medicine the third subject doesn't actually matter and there are no hidden advantages, so don't worry about what subject combo 'looks good' or 'goes together' - choose a third subject you will enjoy studying and where you feel confident about getting an A grade. So Maths won't give you any inherent advantage, and Media Studies (or Art, History, Law, French, English, Drama, Sociology etc) would be just as good as a third subject.