So, riding in NYC -- a topic near and dear to my heart.

Brakes: You'll use them. Believe me, you'll use them -- I don't worry so much about being rear-ended by a taxi as I do rear-ending taxis. They stop suddenly, and for no good reason. That being said, you don't need disk brakes to stop -- you can stop fine with the pads.

Forks: Carbon is just as tough as aluminum, and will soak up some of those bumps that would otherwise go into your hands. The people telling you that carbon is weaker may...not know what they're talking about. All else being equal, carbon is probably a better choice -- just a more expensive one. It's light, it absorbs vibrations, and it's strong. (They build mountain bikes out of the stuff, you know.) When it breaks, it breaks rather than bending, sure -- but if your aluminum fork is bent, it goes on the same trash pile.

Tires: Thin makes you a little quicker, so I always go as thin as I can get. That being said, thicker will help soak up some bumps here and there. But, again, that's a comfort issue -- lots of people ride skinny road tires all over the city, and they aren't breaking their bikes.

And, yeah, you're over thinking this.

By the way (and I know this is the hybrid forum), if you're only ever going to ride on roads, have you considered a road bike?