Gionee X1s has Android 7.0 Nougat and on top of it, Gionee has used Amigo 4.0 as the user interface.
Yes, Gionee X1s does have the front camera selfie flash. The front camera has 16MP resolution and you can get excellent selfies even in dark conditions.
Yes, Gionee X1s does have the OTG support.
Gionee X1s has 4000 mAh Li-Polymer battery. It offers 34 hours of talk time and standby time of 190 hours.