Regarding choosing a tester, I don't know if this will help, but this discussion from the GDC website about their service might give you ideas about what to look for/ask about, etc. http://www.gifteddevelopment.com/About_GDC/gdcexprienc.htm . I would definitely look around on the Hoagies site - I'm sure there's info there as well http://www.hoagiesgifted.org/assessing_gifted.htm
http://www.hoagiesgifted.org/psychologists.htm (list of testers)