Moto C comes with latest Android 7.0 out of the box, so you do not require to update it immediately. However in future, if company releases update you will get it.
No. Motorola Moto C is made of solid Polycarbonate material.
Yes, Motorola Moto C does have front camera flash.
No. The battery is very well optimized and thanks to textured polycarbonate body - we have not come across any heating issue during our review.