If there is any difference, it will be very minimal. You'll probably have more fan or wind noise as there are 2 more fans running. My setup is the opposite and the top are intakes because I want cool air to pass through my radiator. You can set it any way you want it, I just made a decision that I want it as an intake to add more positive pressure to the case.
In a push pull configuration, there might not be enough screws as there are only 8 long ones. Short ones are meant to be used to mount the radiator to the case and nothing in between. You can get additional screws here
if you need more. Pick them according to the thread size and desired length. Too long and you'll have to cut the extra length or risk puncturing the radiator.