Yes, LG Q6 Plus does have the VoLTE support.
LG Q6 Plus has 3000 mAh Li-Ion battery which offers talk time of about 16 hours and standby time of about 200 hours.
Yes, you can change the font size in LG Q6 Plus.
No. LG Q6 Plus does not have the fingerprint sensor but it does have the face recognition lock.