For the Corsair 4000D, you should use the front and bottom as intakes, and the back and top as exhausts. Make sure you mount your CPU cooler such that it's aligned with the airflow. The intake fan should point at the front and the exhaust fan at the rear, it's a surprisingly common mistake to mount the cooler upside down such that it's blowing against the airflow of the case, which will harm cooling. Also don't fill the entire top with fans. A fan at the front top of the case will just exhaust cool air, which is completely pointless. Air should pass a hot component before it gets exhausted. With four fans, I would put three at the front and one at the rear. More intake than exhaust means you'll get a positive pressure inside the case, so there will still be air exiting at the top, but you'll make sure more of the airflow is directed toward the CPU and GPU. Also remove the dust filters from any position that doesn't have an intake.