Off the cuff, that system is very close to the right size. I don't believe that system is too small, at any rate. Does Wisconsin have the need to only run at night to avoid the high summer temps? If so, a larger system might be nice, but I'm betting it's proper for your pond in your area.The Vertex Air3 XL2 comes with 3 double diffusers for a total of 6 - 9" diameter heads. Vertex is a well known brand. I use their diffusers and so far so good (3rd season now). Have you estimated how many gallons your pond has in it? The total gallon estimate, the depths that you wish to run the duffusers at, the lengths of all the hoses, and the pump curve would be necessary to calulate the sizing to a higher degree of certainty. I am not familiar with the pump brand that Vertex uses, but 1/2 hp is proper for that many heads. The spec shows 35 Max PSI which makes me think that it is a positve displacement pump. That is a good pump type for deep ponds or alot of heads.

Don't expect aeation to significantly reduce the muck levels, maybe not even noticable. It will help DO levels.

Fish on!,
Noel