Re: Hardest instruments to play
Hardest string instrument is the violin. Hardest wind instruments are the French horn, oboe and flute, because it takes an immense amount of practice just to be able to make a pleasing sound.
Hardest percussion instrument is the tabla drums of Indian classical music.
Sorry to say, but I don't think the drum set ranks very high on difficulty compared to other instruments. Also, a knowledge of scales, theory, etc. is essential to playing, where it is not on the drumset and non-melodic percussion.