Yes, Vivo Y81i does have the OTG support.
You can record up to 1080p resolution videos on Vivo Y81i. You cannot record 4K videos via Vivo Y81i.
No. Vivo Y81i does not have the removable battery.
No. Vivo Y81i does not come with the earphone in the box. You have to purchase it separately.
Vivo Y81i comes with 5V / 1A charger. It does not support the fast charging.