In order to use my music in your production, you need to obtain a proper license. My representatives can be found on the Contact page. This is true regardless of whether it's a for-profit or charity video.
Yes please! But make sure you credit 'Christopher Tin' as the composer, in addition to the name of the piece, preferably in the video title. However, please don't run ads on the video. Also, if this is a new arrangement of my music, please see below.
If you're creating a new sheet music arrangement of one of my works for public performance (i.e. school concert, church concert, etc.) you'll need to get a simple arranging license from Hal Leonard. If you're a YouTube artist and just want to do an interesting cover of one of my pieces, then great! Go right ahead, but there are a few restrictions:
It's a convention borrowed from the film scoring world. When you're recording scores for film, TV, or video games, the orchestra players don't get a chance to practice the music before the session; they just show up and sightread it. Omitting key signatures and just putting the accidentals in the bars makes it easier to sightread, particularly for pieces that are highly chromatic, or modulate frequently.