I would call the guys at Sweetwater. They are great and can talk you through all the stuff you will need. Christian Good is a great guy and was really helpful in getting us set up three years ago.

You will need to buy speakers, sound board, microphones, cables, amps (if passive speakers), a power source (generator or battery system), wireless system (optional), and then a speaker cart to throw it all into. Highly suggest Stadium Creations for your cart.

Lastly, if you have a kid that plays piano decent, then you will need a synth. If you don't and you plan on having percussion students play a synth part, look into buying a MalletStation. This will allow your percussion student to continue to develop as a percussionist and not have them pecking at notes on a synth. There are cons to it, mainly you will need to buy a computer and the malletstation can be a bit finicky.

But like I said, call the guys at Sweetwater!