LG Q6 Plus dimensions are 142.5 x 69.3 x 8.1 mm (W x H x D).
Yes, you can change fonts in LG Q6 Plus.
Yes, LG Q6 Plus does have the ViLTE support and you can make video calls.
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.