If you use the supplied 5W charger, it charges to 18 percent in 30 minutes and 35 percent in an hour.
Yes, Redmi 6 is a VoLTE phone.
No. Redmi 6 does have a dedicated MicroSD card slot and 2 other slots for SIM cards.
Yes, Redmi 6 does have the ambient light sensor.
If your budget absolutely can’t exceed the Rs. 8,000 mark, go with the Redmi 6 without any concerns whatsoever.