CFM case fan flow suggestion clean in clean out

Hello, I like to pump filtered air into my rig, this creates an overpressure situation. The reason for this is to fill the case with clean air and the extra air will flow out all the silly holes without caulking. I would like to have lattitude to write how to operate in a contaminated environment (MIL SPEC.) but that is classified. So, my desire is to force filtered air into the case via 1 or more fans with an easy access filter element on the side of the case. The case side because ease of access to the filter elements and the fans can blow toward the motherboard. (Don't want to disrupt air flow at CPU fan) My case is about 4 cubic feet, therefore 40 CFM would exchange the air 10 times in one minute minus filter resistance to flow; 40 CFM probably not enough need engineers input. I prefer to pump filtered air into the case that keeps dust from entering the case. The more you seal a case the finer the dust that gets in, save money and maintainance fill the case with filtered air. Do not caulk the case because if the fans fail you will end up with a beef jerky smoker. So, my intent is to install enough fans with filters blowing into the case so that all the air escapes out the vents and cracks dust free. I do not want a top vent because my bro's energy drink spill will run down Mobo liquid in smoke out! If you blow filtered air into the case, and the air flows out of the case, and the temps stay right that should keep your rig clean and happy. Imagine a dustless case system 'pat pend' etc. Feed back welcome.