No. LG Q6 Plus is not a waterproof device.
Yes, LG Q6 Plus is a metal body phone.
No. LG Q6 Plus does not have the fingerprint scanner but it comes with advance level face recognition.
Yes, LG Q6 Plus does have the face recognition. You do not even require to power up your phone. It's camera automatically detects your face and unlocks the phone more quickly than typing, drawing or fingerprinting.