Your big concern with the setup, I think is that you want to have an in and out fan beside each other,
Your best bet will be to pipe in the outside air to the back side of the room.
You could likely run 2 5" dryer liners in over and down the back wall, and get away with a large exhaust fan.

As for the CFM you are after, you will never get a silent version. That's going to be hella noisy lol