No. You cannot change the color of the notification light in LG Q6 Plus.
Yes, LG Q6 Plus does have the Google Assistant.
Yes, LG Q6 Plus does have the VoLTE support.
LG Q6 Plus dimensions are 142.5 x 69.3 x 8.1 mm (W x H x D).
No. LG Q6 Plus does have the LED notification light and it also has the Always-On display.