I've got an idea for the front windows, in terms of protection from stray rocks. Look into a product called "clear bra". People swear by it on $100k+ vehicles. Won't help if you sling a 3lb rock towards it, but should do the trick for road debris and such. Shouldn't be able to tell that it is there from the outside and won't affect your window tint on the inside.
I would also look at using ceramic window tint to help keep even more heat out. I imagine that it will be an oven in there with high temps outside.