could you give us some more information regarding the room you plan to use? what size is it. IE height/length/width. No one could give you a good answer without at least those factors.
Me personally, I'm using my 400w hps in a closet that measures 4 feet wide 2 feet deep and 6 1/2 feet tall. For this room I'm using a 75 cfm duct boosting fan, a regular 14 inch oscillating fan, and my hood is enclosed/aircooled. So far my temps have been staying at 76-80 degrees faranheit.
Its important you think of your ventilation system as a river. At least I do. I think of it like this because in the natural world both water AND air flow, through the path of least resistance best, so once you have your venting setup, make sure you have the least amount of bends and turns in it as possible, in order to not restrict airflow too much.