Nokia 8.1 has a double channel LPDDR4X type of 4GB RAM.
Yes, Nokia 8.1 does have NFC support.
Yes, Nokia 8.1 display works as a flash under low-light conditions.
Yes, Nokia 8.1 comes with headphone in the box.
There is no official communication from the company if Nokia 8.1 will be able to work on the 5G network or not.