The fact that you chose to host an undeclared guest for several nights broke the Airbnb's Host Guarantee conditions, leaving your stay and the property uncovered.
Regarding the Netatmo Welcome Security camera present in the entrance of the accommodation, its presence is mentioned in my House Rules, in the Airbnb chat message I sent you a few minutes after your booking, allowing you to cancel without any penalty. And there was and there still is a picture of the camera in the description of the accommodation. I thus perfectly abide by the Aibnb's rules regarding cameras.
CAMERA -Rules for hosts
If you’re a host and you have any type of surveillance device in or around a listing, even if it’s not turned on or hooked up, we require that you indicate its presence in your House Rules. We also require you to disclose if an active recording is taking place. If a host discloses the device after booking, Airbnb will allow the guest to cancel the reservation and receive a refund. Host cancellation penalties may apply.
Regarding your early check-in request, I let your friend enter when he arrived.
3pm is the check-in time allowing the cleaning to be performed. This check-in time is clearly stated in the message you received a few minutes after your booking and was confirmed in the answer to your questions and was available and explicit before you booked.