No, I don't leave windows cracked open
1. My car has a light colored leather so it stays at least a tiny bit cooler then dark leather.
2. I used to have all but the windshield tinted, (up till I got ticketed for it, even though it was like it when I purchased the car) The tint blocked a lot of the light, and kept the car significantly cooler. This was up to a month or so ago, so I'm still adjusting to having to wear sunglasses, etc. The rear windshield, and rear side windows are still tinted, so aprox 50% of the window surface doesn't let more heat in.
3. What if it rains and is very windy?