Have you talked to Jeff at Freeze Frame? He can probably help more then anyone. The resolution on the cameras that you linked to is not that great but will get the job done. For tech info the site kind of sucks but they are claiming 30 fps (frames per second) that is likely divided by the 4 cameras if you go that way. So if you use all 4 camera ports then you are only going to get 7.5 fps. So if you want good video that is not jerky then you will want to run no more then 2 camera's off the unit. That is the bigest cost when we get into larger survalance systems for comercial and larger houses is just dealing with all the information that comes into the system from the camera's. The system does look nice and well thought out I would just find out if the 30fps is each camera or total.
If you want I can make some calls Monday and see what I can find out for you.