Exhaust has nothing to do with how close you can put your light. That is unless you are using a cool tube or a vented hood hooked up to your exhaust. Lights "throw" heat as well. Some throw more heat, some less. Hps throws less heat then mh and cmh even less then that. So most use the back of the hand method as to how close your light should be.
Do not get a 1000 watt for that box or you will have problems with heat. A 600 will do fine. Get a 6 inch vortex and yes they make lots of noise. Get or make a duct muffler, mount fan in box, ballast outside. The bulb makes noise as well.