Any idea which species of sunny you caught and transferred to your pond? In MN there are a few options.

Bluegill
Pumpkinseed Sunfish
Green Sunfish
Longear Sunfish
Orangespotted Sunfish
Warmouth

Most like candidates are the bluegill(BG) and the punpkinseed sunfish(PSS), either is fine for your pond. Green sunfish(GSF) can be a bit more of an issue, but with bass and pike present they shouldn't cause an issue.

I too feel the initial numbers stocked were reasonable for creating a good fishery with adult fish. The only other species you can consider would be yellow perch. Hopefully the fish will over winter without issue. The fact that a wetland with the large amount of water seems to have only had fatheads to this point makes me believe it may be prone to winter kill. This is where adding an aeration system may be worth the expense...