Yes, Redmi 6 does have GPS support.
No. Redmi 6 does have a dedicated MicroSD card slot and 2 other slots for SIM cards.
Redmi 6 comes with 5W charger.
Yes, Redmi 6 does have the AI face unlock functionality.
If your budget absolutely can’t exceed the Rs. 8,000 mark, go with the Redmi 6 without any concerns whatsoever.