Perfect. If that CPU is stronger enough to run
blue iris it will save you tons of $.
AirPort Extreme is fine since u have a computer for the nvr. Google how to set up a VPN server on the the computer. Not a client but a server.
Get 4 turret style cameras off allieexpress for $70 each. 4mm or 6mm just not too wide angle or you will be able to get details in a subject to tell police. I like the 4mp Dahua. They are super sharp and not expensive. Very good dynamic range. Dahua has color day and black and white night vision that works well. Add a few trip sensors or infrared sensor to send you a push notification.
Mount cameras low enough that you can get a good angle of someone's face vs too high that you see a guy in a hoodie.
Remember this only helps with identifying a subject or the scene. It won't stop a crime. VPN is essential if you don't want others to be able to access or hack your cameras if they are setup for remote viewing.
Get a POE switch to power cameras through the Ethernet wire for simplicity and stability. And clean install. Pull
cat5 Ethernet to each camera install location and back to server.