Nokia 8.1 comes with the Android Pie out of the box. You will also get Android updates for the next 2 years.
In the official packaging of Nokia 8.1 - you will get your Nokia 8.1, USB Type C cable, Power adapter, Headset, Quick start guide & SIM door key.
Yes, with Nokia 8.1 you can record 4K videos @ 30 fps.
There is no official communication from the company if Nokia 8.1 will be able to work on the 5G network or not.