Yes, Redmi 6 does have a dedicated MicroSD card slot.
Yes, Redmi 6 does have the ambient light sensor.
No. Redmi 6 does not come with the earphone in the box. You need to buy it separately.
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.