Oh boy, the students are going to seem like babies to you at first.
I used to teach HS and MS. Then I changed to elementary and love it. It is a big change though.
I like the idea of musical rewards. Maybe you could have them earn the right to play, "Guess That Song". You could play a small song bite and then have them guess the title of the song, what movie it is from or who sang the song. Just an idea. Elementary kids like guessing, especially when they are correct.
You might also Google music riddles. The students could earn the right to answer a riddle at the end of the period. I do a riddle a day in my third grade class and they love guessing the answer.
Sorry, I can't help with your other questions as I am not a musical person.
How about incorporating some movement and dance? They will behave better if they can get some wiggles out. This is especially true of the little guys. It will also teach them about rhythm.
You might also check into musical field trips. Our fifth graders go to a short version of the city's symphony each year. Our third graders attend a shortened version of The Nutcracker. Both are sponsored by large businesses like Target. Our students just pay about $3 to cover bus/transportation costs. Just an idea.
Our music teach also has each class perform a grade level concert for the school and then that same night again for parents. It is really good experience for them to get on a stage and perform. The parents love this!
Good luck! Best wishes for a wonderful 2012-2013 school year.