Backyard Aquaponics
A place to discuss aquaponics

I, see were your quoting your outside demensions for your GH, but the inside demensions are going to be 7" less than the outside using 2x4 framing. In other words 11'-5" x 15'-5" and that's is tight. So the 3 tanks that you are using along the back end wall may not fit the way you want.

Best to take the drawing of the whole thing, and remove all the wood from the door back to about 30" from the back wall and it will be clearer.

I see this same thing in a lot of designs, they think that the inside and outside demensions are the same, but forget to subtract the wall thickness's. But it can happen that way if the wall thickness's combined are as thin as the sheet of paper your are reading this from.

If you plan on high fish densities then all bets are off and you're going to have to add aeration.
If you're not planning on high stocking densities then you don't need additional aeration but it's good to plan in some splashing at outfalls, and a venturi is good as well (the more the better). Some people use spray bars for the flow going into the fish tank as another way to get aeration. In one of my systems the water is pumped from the sump where I have about 8 different outfalls so it's pretty well aerated by these before it goes back to the fish tank. There is also a venturi on the inlet to the fish tank.