Wow, a lot of questions.
You have already placed the cast shadows of the trees, and shrubs. Based upon those cast shadows, it seems as though the light source is located behind, and to the left of the subject, because the shadows are being cast to the front, and right of the trees.
This means that the entire front of the figure is on the shadowed side of the subject. In such a case the butterflies would not be casting any definite shadows. However, there would appear to be darker areas under, and around each butterfly, but they would not be of any definite shapes, or directions.
I'm not sure that a unifying glaze will contribute to this painting, but if you choose to apply such a glaze, the following would be a good suggestion:
Apply your painting medium to the surface of your dried painting, and spread it out into an extremely thin application, using your fingertip, or a small, cosmetic sponge. Then, apply paint directly into this applied medium using the medium as a lubricant to aid in spreading the paint out into a very thin layer. Use a large, flat brush to do this. I am not sure what color to suggest for this glaze, but that is the procedure I'd use to apply it.