You really don't want to mess around with this without consulting a lawyer first. A misstep could mean committing multiple felonies and possible jail time.
Never talk to a lawyer until money is about to change hands. More good ideas are killed, deformed or outright stolen by lawyers than by any other means...ever.
Right, hence my saying that it will be ficticious in its initial incarnation.
As long as you're not taking in real money or paying out real prizes, you're OK. It is actually illegal in some states to pay out real prizes even if the entry is free due to sweepstakes laws, and there you get into the 'consult your laywer' area. But even then, the odds of anyone ever prosecuting you for giving stuff away are virtually non-existent.