Yes, Redmi 6 does have the 18:9 aspect ratio full-screen display.
Redmi 6 is made of industrial grade polycarbonate material.
Yes, Redmi 6 does have the FM radio support.
Yes, Redmi 6 is a VoLTE phone.
If your budget absolutely can’t exceed the Rs. 8,000 mark, go with the Redmi 6 without any concerns whatsoever.