We have three mallards here and they are fully flighted now. They free range late in the day till dark with our chickens, and occasionally fly around the yard. Last night, they flew in the opposite direction, towards the trees and forest on our property. As soon as they saw the trees, they freaked and scattered mid-air. I was terrified lol. I ran out and around the fence and into the trees. Found two of them, but didn't see the third. She was about 30 feet or so down the fenceline. All three were still as could be, they had NO idea what they'd done or where to go lol.
Your little one, as he begins to get his flight wings, will definitely be able to fly over a 4 footer. Our run is 18x24 with a 6 ft. fence and they easily come off the ground and over it into the yard.
As to your question about his wings...I don't have an answer but am going to hang around for it. We're debating on this, as well.