NSO music : Well, as i know harmonium is not a part of NSO music. ( I was in NSO tabla
) but you have other options like tabla, guitar, vocal, violin, key board .
Swimming : it is an excellent option to maintain fitness.
Badminton : selections are a lot tough.
Volley ball : You can be selected even if you know a little bit of the game.
NSO music is infi chill course and you would pass if you just have a good attendance.
well, you can prefer any thing. Go for the thing which you want to excel in ( you can excel only if you know a bit of it.)