Yes, Oppo F9 does have the GPS support.
Yes, Oppo F9 does have the dual rear camera set up. The main camera has 16MP resolution while the second rear camera has a 2MP resolution.
Oppo F9 has a dual rear camera set up, 16MP and 2MP. The main 16MP rear camera has an aperture of f/1.8 while the second 2MP camera has an aperture of f/2.4.
No. Oppo F9 does not have the front camera flash but it does have the display screen flash for the front camera.
The most striking feature of the Oppo F9 is the big display with the waterdrop notch. It is well designed, delivers good battery life, and offers decent performance for the price.