I agree with Mr. Poulson although I would really suggest that you hire a lawyer to advise you.
I agree with Mr. Poulson and Ms. Johns. You really need to invest in the business and get legal advice on the issue. I really think that the issue which will cause you problems is if the "Prizes" are real versus virtual. I play online poker and there doesn't appear to be a problem (based solely on experience) with the sites where you are given chips and can buy additional chips and win virtual prizes. That is not the same as being able to turn those virtual chips into real world cash like items. You definitely need to consult a knowledgable attorney about the legality of that issue.
Yes, I do agree that the attorney consult is the only way to be sure, and a must befoer proceeding.