1) 25 mm. 100 psi front and 115 to 125 psi on the rear works great for me. I've tried lower and I'm slower and more worn out. And I've tried this many times for at least a dozen rides together. Plan to go to 28 mm but I still have 25's on the shelf.
2) 4000 plus maybe on the bike I just gave away. But tire mileage on it wasn't tracked well. Current bike has 3000 miles on it's tires. All still good tires.
3) Never had a flat on them yet that I can remember.
4) Smooth to very smooth asphalt with aggregate less than 3/8" and less diameter. Potholes certainly, but I go around those.
5) I like to keep my best tire on the front. Between the front and back, I'd rather the back go out from under me and cause a crash than the front go out from under me. Remember that as long as the wear indicators put in there by Continental are visible, the tire is good. I prefer the wear indicators of all tires, when the cords of the casing show and it gets a flat.