If you want more airflow and youre serious about cutting the bonnet then its no problem. Id say just above where the airbox is, would be perfect. a 19 scoop would work a treat.
The other thing is what goes in must come out. You wanna think about cutting in an exhaust vent at the rear of the bonnet to let the air flow properly through the engine bay not just into it. In fact if there is no decent route out, not very much air will go in, its basic physics.
The only problem is how to stop rain getting in there when the car is at standstill. A decent undertray under the exit vents which drips the water down through to the ground would do the trick.