Yes - saw multiple couples having professional pictures taken in the sunflower field the day we were there.
Yes, you may, but if it's the sunflowers you're interested in, forget about it. The blossoms have long since gone by. Just address of tall stalks remain, of course,laden with sunflower seeds. Better luck next year. But by then they will have figured out how to charge you to take a picture.
Yes. No permission needed.
I don't know. Better you ask them.
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