The only way to tell is to cut him up and weigh all the fat. Anything else is just a guess, and means very little. For the most part, BF% is an arbitrary number.
I'd ditch the idea of "cheat meals" and try make your diet more flexible. If you want to up calories one day, it won't do much harm. You could argue you don't want massive deficit on deload due to...
You can if you want! People just always tend to have the desire to continuously build on what they have. But if you reach a point where you are happy, then that is great!
In saying that, I actually like Taubes. I think he is actually a smart guy, I just think he has an overly simplistic, and arguably incorrect, view on what causes the obesity epidemic. It is likely...