Probably a good plan to ask at the school where you will be continuing your studies. They will likely give you some idea of apps that are good to have. Be sure to explain that you have a Mac, as that can make a difference in the recommendations for study materials.
For your downloads, if you are concerned about filling up your internal drive, you could copy your large files (movies, etc) to and external drive. Connect the drive when you want to watch movies.
Or, you could just download the movies at the time you want to view them....