No. Vivo Y81i does not come with the earphone in the box. You have to purchase it separately.
Yes, Vivo Y81i does have the OTG support.
Vivo Y81i is made of Aluminum Alloy and industrial grade polycarbonate material.
No. Vivo Y81i does not have the removable battery.
Vivo Y81i has FunTouch OS which is based on Android 8.1.