Yes, Redmi 6 does have a dedicated MicroSD card slot.
Yes, Redmi 6 does have the ambient light sensor.
Yes, Redmi 6 does have the 3.5mm headphone jack.
Yes, you can play PUBG on Redmi 6.
If your budget absolutely can’t exceed the Rs. 8,000 mark, go with the Redmi 6 without any concerns whatsoever.