Good stuff, VT. If I may add...
4. Song selection. Choose songs that the young people can learn fairly easily (e.g. a Hezekiah song). This will boost their confidence and build their excitement about learning new songs, plus it'll make things easier for you and help you to ascertain their skill level). After they've mastered a few easy songs, you can introduce other songs that are a little more challenging. Whatever you do, don't try to make them learn a song that is significantly beyond their current skill set just because the song is hot or everyone is singing it.
5. Praise openly and frequently, rebuke privately and infrequently. If they're doing great, don't hesitate to tell them over and over again. In time, they'll look for that approval. Young people thrive on getting the approval of adults they respect. They'll strive to do whatever they gotta do just to see that pleased look on your face and hear you say "good job."
6. Let them take turns opening in prayer. This will give them a sense of ownership in the choir.
And I wanna REITERATE VT's #1. That is just sooooo important. It's worth repeating.