Actually, 50cfm is practically nothing, but for your space it might work... It's always good to have too much than too little ventilation.

360w of cfl in a 6cf area is probably going to get pretty hot. Test your setup before you start planting anything so that if you need more ventilation, you can add it. Temperatures should be 70-85 degrees F. Too far below 70 or above 85 will stress the plants and reduce your output.