Yes, Moto G5 does have gyrosope sensor.
No. Moto G5 does not have front camera flash but the display flash is there, which is as powerful as LED flash.
Yes, you can update this phone. However, this phone comes with latest Android 7.0 Nougat out of the box. So, you may not require to update the phone immediately.
Moto G5 3GB RAM variant has 16GB internal memory.