You're going to have to experiment, no other way around it.
That said, I would imagine a fan(s) at the front to do a whole lot of nothing; there's just too few places for air to get in with the way that panel looks. Make use of the areas that are easiest for air to pass through first, which is the top and rear:
A)2* top exhaust fans and the rear also exhaust, thus forcing a negative pressure setup, which creates a vacuum(of sorts) that will draw in air from every other possible opening.
Consider removing the PCIe slot guards below the gpu for added effect, except if you have nosy kids or small pets.
B)Flip the rear fan to intake, and set 2* top exhaust fans. If the cpu cooler is a tower(stands straight up), flip the fan(s) on it to...