You will have more success from a monetary standpoint if you practice hard and get as good at your instrument as possible. Staying in music academia may help you with that, and a more advanced degree will let you adjunct as well as play gigs (and charge more for giving lessons). I have quite a few friends who have made an acceptable living as musicians through a combination of teaching and gigging. It's almost impossible to get a job as a history professor, so don't go into it for that reason. Obviously, it's a fun thing to study if you want to study it. You could ultimately also do some academic research and publishing if that interests you. A lot of working musicians also do that.

Hi there, for starters good for you! A postgraduate degree is always a good thing to consider.

The answer here is that where you go and what you want to specialise in is very much up to you. Furthermore, because a postgrad is much more intensive your field will require certain skills upon entry, primarily linguistic.

I finished my Master's in Byzantine Studies last year at an intercollegiate program in London and for that we were taught Ancient Greek. But needed French, some German and a little Latin. If you do Nazi Germany obviously you don't need all these. It depends on you and what you want to pursue.

For your field, read the general histories sure but start to get a grasp of historiography. Your seminars will not be telling you events they will be approaches towards them, the facts must be known before you start the class.

I hope this helps