Sorry but that is how you appear to be coming off time and time again. It makes communicating with you very hard. You may not mean it that way, but when you first started posting you were not quick to take advice and were quick to point out all the money spent on Koi and ponds and plants and landscaping. I was very nice in how I expressed the fact that you come off snobbish. There is no need to list all your degrees, they have no impact on here, typos are made by everyone and frankly if someone cares about typos they need a reality check on whats important. Everyone on here is here to learn and share knowledge of how to best care for ducks. I could list all of my background, but seriously it doesnt matter except for the fact that my background includes animal science and vet training.
so back to the subject at hand
Your enclosure is nice, i would remove the shelves they are pointless for the ducks you have. I would sell of multiple pairs and keep 6 and no more in that enclosure. Replace the shelves with multiple nest boxes for them to select from. Plans for propper nest box houses can be found online for wood ducks. (dont confuse them with wild bird houses or chicken nest boxes)
The mallards should be netted and sold, just because they can fly doesnt make it right to let them be released. Just because someoen else does it, also doesnt make it right.
Feedin I think you are over thinking, it is great to offer a variety, but as I stated before you dont need to blend the three commercial feeds together. mazuri is fine on its own and add in seeds, fresh green, bugs ect.
Netting the unwanted or over populated small baby fish from your pond is a great way to population control and provide a free food source to your ducks. I say go for it. They will love it, you will not worry about the fish pond becoming over stock, thats a win win
Feed only enough to be cleaned up in 1 day, re-feed the next morning. If it rains and blows into the enclosure, be prepared to toss the wet feed and replace with fresh dry feed.
You live where it snows. Best plan now how you will provide wind breaks and stop snow drifts from blocking your access to the pen, and from effecting the pond as they will need the water all winter too. You dont want to fully close off the pen as you also still good air flow for ventilation. Just good to plan ahead and have the panels on hand to help provide shelter from winter elements.