@Nicky89 When I have had guests not answer repeated messages, I've contacted Airbnb and they have gotten in touch with the guest and I then got a return message from the guest.
Yes, I think your concerns about this booking are valid, and I would also tell Airbnb that you have a feeling this guest is planning to throw an unauthorized party. I'm not sure they'll be amenable to you cancelling without penalties, but I'd be firm with them about it having all the earmarks of a party- local, zero communication, New Year's Eve , and at least it will be on record that you wanted to, and if it turns out to be a party scene, there will be some backstory that your suspicions were correct.
I assume you have some cameras and a co-host nearby that can keep an eye on what is happening there if you don't cancel?