I found a cool website and answered one of my questions. Here is info on the weather;
http://www.nps.gov/acad/planyourvisit/weather.htm

What about the flies though........?

NEWLYWED: I've been assured that the "black flies" stick to their hangouts. If you read the other posts you'll know where they are: water holes and woods mostly. I'm going mid-june as you know, and I feel confident we'll be OK. I'll just be happy to be away anyway!

We decided to "chance" it and we're going in June. Hooray! Thanks to this board for guidance!