I've listened to your recording a number of times, then had my 10 year old listen. He said, "It was good when you were just singing it." I think he has a point.

There a bit too much going on, and it gets in the way of the melody and the lyrics themselves. I think a closer unison between the recorder and the voice could simplify things, and I think those fifth on the concertina could be used more sparingly.

Long ago, when I was learning to arrange(actually, I am still learning), it was suggested to me that when harmonizing a melody(which is really what you're doing) a good default was to start with the chord fundamental and to hold onto it as long as possible, and then to move to the closest possible note that sounds good.

Even in composition class, the ear, and not the theory, is what decides.

In theory, we think in terms of dominant and subordinate parts, and we try not to put things in the subordinate part that overshadow the melody. At least not too often....