I'm not an expert on this area, but I think you would need an Entertainment licence to do so. There may also be breaches of H&S laws if you do not provide toilet facilities.
Bear in mind that if the police become aware of the rave, they can and do have the power to terminate it.
You also might want to consider insurance (what if someone gets injured?)
Environmental health may get involved if the neighbours complain as well.
I'd be inclined to think very carefully through all the pros and cons before letting possibly hundreds of youngsters onto your land for what could be a 3 day party. And think of the mess afterwards!