Pileus

Yes, looks like a Northern Harrier. I get the impression of facial discs from. It bugged me that the tail seems short, but that may have to do with the perching angle of the bird.

I think you have American Wigeon in flight, and the duck second nearest in the bottom photo is a Wigeon. The nearer bird in the bottom photo appears to be a Northern Pintail, as does the nearest bird on the water in the next-to-last photo. The bird back left of the Pintail on the water in the next-to-last photo appears to be a Wigeon based on the head shape and white patch near the rump.

Yes, it is a male Ring-necked Duck. As a fellow Missourian, I can tell you that they are common throughout Missouri in February. The second bird is a Horned Grebe, which are also present in Missouri in February. Among other field marks, a Western Grebe would have a longer neck and much longer bill. Your third bird is an American Kestrel.