I agree with Adrenaline - we actually just covered this in my law class (I'm taking Business Law at a local college to brush up on my busines skills). Adrenaline's right in that if the non compete clause is seen as 'interfering with the teacher's right to make a living', it won't be considered in court.

Courts will enforce a no compete clause only if they think its "reasonable", which usually means no more than a radius of 3-5 miles away from your studio and for a length of time of no more than 2 years. As far as keeping your customer list confidential, I'm not sure if there's a way to word the contract so that it states you can't steal the customer information or 'trade secrets'.