Let me preface this by saying I wasn't aware of any of Mark's FChat 'antics' before the link was posted here in another thread, but I can say that in his recent posts on LamboPower in their McLaren section he's been fairly enthusiastic about the potential purchase of a 12C and I don't suspect he has come here with the intent to cause trouble. Maybe we give him a chance?
To answer the questions, even though I exemplify one of those "kids who were not even close to being able to buy a (in this case) McLaren"...
The general theory, and the one being promoted by McLaren, is that if you don't plan for much if any track use the standard steel brakes are the better choice. They also end up being lighter which is somewhat counter intuitive. Cost of replacement is much lower and there's no concern of chipping the rotors when mounting wheels on the car.
Some have raised the concern that the steel brakes lack the cooling vents in the front that are included with the carbons, but we can assume McLaren have done their homework
here in the decision to leave them out. I have yet to see anyone complain of brake fade under high temps with the steels, unless they have done so in the owner's section.
Sport exhaust is more about sound than any real performance benefit - perhaps you'll have the opportunity to sample both as it seems that would be the best way for each
individual to decide. If you know you like a bit more sound from your car it is probably necessary as that why it was originally created.
Hope this helps, and maybe chills the mood a little.