Yes, Gionee X1 does have support for VoLTE.
Yes, Gionee X1 does have the USB OTG support.
Yes, with the help of App Clone functionality, you can use 2 WhatsApp accounts in Gionee X1 at the same time.
No. Despite of having huge 3000 mAh battery, Gionee X1 has not reported any heating issue during our review.