My mind is wanting to treat this pond as two 1.4 acre ponds. The deep half (on the left) is pretty straight forward, but I would have to lean on someone with experience in what you have going on in the shallow half. I'm just not sure what can be done with that much shallow water or if it would be worth messing with.

I assume you meant that the deep half "averages" 9 foot and that it has deeper waters than 9 foot. If this is true, you need to look at a centrifugal vane pump or a piston pump as they will pump the air into deeper waters than the cheaper diaphragm pumps. Actually, even if your deepest part is at 9 foot, I'd still advise the centrifugal vane or piston pump, but that might be a difference in personal preference and/or the actually depth you choose to place your diffusers. I'd design the system to be able to put the diffusers on the bottom and be able to move them up in the water column if desired rather than be locked at a 4 to 5 foot depth to begin with.

Fish on!,
Noel