Traditional airflow is front, bottom and side in with top and back out. Modern GPUs sometimes benefit from the side vent fan being an exhaust.. and sometimes side intake and bottom exhaust. In most cases 2-3 intakes and 1-2 exhaust fans are plenty. I like to have a little more intake than exhaust because this give the case just a little more pressure inside thus keeping dust from being sucked into all the plugs, sockets, optical drives, etc.
My personal case has 3x 140mm TY-140 intake fans speed controlled by PWM signal from CPU fan socket.. same as my CPU cooler fans. All idle at 660rpm and max load at 1050rpm. My wife's case has 1x 140 & 1x 120 intakes PWM controlled by CPU fan socket and idle at 700rpm with max load at 1200rpm. I've helped 3 others build similar setups. 2 of them have the bottom intake PWM controlled by GPU PWM signal. Controlling case fans this way means they speed up moving more air when the CPU and/or GPU need more air to stay cool but idle down and are quiet when CPU and/or GPU are not working.
Advantage is systems are quiet when doing light load to medium tasks and only speed up when the work load increases.
My personal case has 3x 140mm TY-140 intake fans speed controlled by PWM signal from CPU fan socket.. same as my CPU cooler fans. All idle at 660rpm and max load at 1050rpm. My wife's case has 1x 140 & 1x 120 intakes PWM controlled by CPU fan socket and idle at 700rpm with max load at 1200rpm. I've helped 3 others build similar setups. 2 of them have the bottom intake PWM controlled by GPU PWM signal. Controlling case fans this way means they speed up moving more air when the CPU and/or GPU need more air to stay cool but idle down and are quiet when CPU and/or GPU are not working.
Advantage is systems are quiet when doing light load to medium tasks and only speed up when the work load increases.