#2 - Not a lot of districts care to pay for success of the band program. You can certainly include in your presentation that you've done x and y with the band program. This is generally a good way to get increased budget or a one-off budget for new uniforms or something, but not for your salary.
#3 - The more effective argument will be comparing to other districts. Nobody likes to be at the bottom of the pile. It sounds like you've already done some research, but I would definitely put together some numbers about what districts nearby are paying their band director (make sure you include teacher base, stipend, contract length, extra days) and see where you end up. If you're in a 2A, don't worry about the 6A districts. Don't compare to districts on the other end of the state. Compare apples to apples. A good place to start is the schools you compete against in your UIL region.