Greg G, Looks as if you have done very well! For $90, super!
The motion blur on the ball and racket look very small. You can farther evaluate motion blur by taking close ups of the racket and ball.
Have you found anything in the user's manual (Casio 200 pages) that describes what you have found regarding the HS button and getting faster shutter speeds?
I like the behind view for showing the serve. You should see all the details and some important angles. Direct sunlight also shows the shadows, for example, shadows on the elbow bones that are helpful in analyzing the upper arm rotation on the serve. https://vimeo.com/21512296
I have just recently discovered that Youtube now will single frame using the forward and backward arrows. Before it didn't.