Martha -- I fear the heat, as well, but having survived (barely) the full this year, I feel like the Minnie shouldn't be too bad. Don't forget the start time is about 6:15, I believe. So you'll be done long before it gets too warm or the sun gets too intense. I do remember being very happy last year to have a visor. If I remember correctly, I think there was a lot of fog early on and that helped, too. I do know I was very, very glad I wore a visor to help with the sun in my eyes and on my face, generally. I bought a cute white one with the Minnie Marathon logo on it and have added that to my packlist for this year.
I just bumped up the Minnie race reports thread from last year so that everyone can see Mel's great pix of the course, etc. I don't remember who else posted race reports but I am sure there is a lot of valuable information there.