Yes, Redmi 6 does have a dedicated MicroSD card slot.
Yes, Redmi 6 does have the FM radio support.
Yes, Redmi 6 is a VoLTE phone.
If you use the supplied 5W charger, it charges to 18 percent in 30 minutes and 35 percent in an hour.
If your budget absolutely can’t exceed the Rs. 8,000 mark, go with the Redmi 6 without any concerns whatsoever.