Yes, Vivo Y81i does have the OTG support.
Yes, Vivo Y81i does have a dedicated MicroSD card slot.
Vivo Y81i comes with 5V / 1A charger. It does not support the fast charging.
Vivo Y81i is made of Aluminum Alloy and industrial grade polycarbonate material.
No. Vivo Y81i does not have the front camera flash.