I assume your son is interested in going anywhere in the country. Headfirst is a great showcase, it has a wide range of schools academically, geographically, and baseball-wise, all under the "high academic" umbrella. If you go to the Headfirst website, you can see which coaches are signed up for their various showcases. I agree that you should be in touch with some schools ahead of time, with intro email and video, but the good thing is that you might also be contacted by schools you'd never considered. I also think that, with these schools, it doesn't hurt to ask if your son's high school or legion coach would contact them and put in a good word.
If your son prefers to stay fairly local anyway, then you can probably get in front of in-state or nearby-state D3 coaches at a more local (and cheaper) showcase; in some states PBR will do that for you (not a waste of time and money the summer after junior year, depending on the state and the showcase).
As Smoke said, high academic D3 coaches spend the summer watching players at these showcases, in games, and at their own camps. They start inviting players for campus visits in mid-late August, and often offer admission help at that time (slot, or whatever). Arizona seems a bit late in the cycle, if that's all you're doing.