Yep. Had a little fun reading through this one. A lot has been said, but not much that is important to my considerations.
I have kept American Games most of my life so will vouch for their ability to survive in as feral populations. They will out perform the breeds on your list when is comes to surviving and reproducing. You may find it prudent to augment nesting habitat. All breeds that are small or like bantams will more be aggressively targeted by raptors when area dog must protect is three acres. Silkies have no business being outside without direct human protection.
Where I work we he have an experimental Elder Berry plot on about 1/2 acre that is adjacent to a similar sized native plant display. I have a group of chickens used for public display that is occasionally released into both plots. Group is a harem made up of 1 or 2 hens, 6 to 12 chicks / juveniles, and a harem master (cock). Giving choice the chickens drift towards the native plant display relatively quickly. While the birds work the Elder Berry plot the have three type of micro-habitat to forage. First is the Elder Berry plants themselves which support modest amounts of insect drift the chickens can consume. The insects that are problematic such as the evil beetle below the chickens will not touch.
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Chickens will work the mulch area and might provide some benefit by bioturbating mulch reducing abundance of some critters that do not tolerate bioturbation well. The chickens do also eat a lot of mulch inhabitants that are not toxic as enabled by consuming the Elder Berry plants.
Chickens will be most impactful on insect communities and possibly slugs within cover crop between rows. The chickens can easily reduce the insects growing on location as well as the drift.
Supplemental feeding of chickens can be used to get more even foraging pressure on the entire 3 acres. Too much bioturbation of mulch may be problematic for the Elder Berry plants so watch that.
I work at a land grant university where my lab sits in the middle of several cropping systems. This makes me think that trap crops might make the chickens more effective at controlling some pests. Pest like the Elder Berry Beetle and Spot-winged Fruit Flies are not likely to be controlled owing to toxicity or chickens not interested in such small items that stay largely up and out of reach.