You do not drive a Formula 1 race car, you do not need to fill the tires with Nitrogen. It causes the tire pressure to not fluctuate as much under heat, but it's not that big of a deal.
18s will handle better because there is less tire widewall to flex when cornering hard. I think your friend is just jealous. I'm not sure what the weight difference is.
I have a '68 Fastback GT with Deluxe Interior, below you will find a picture of the turn signal lever in question.
I was told this is not the original lever. Does anyone know whether it is or not? If it isn't, what is it from? It was pretty rusty but once I polished it up it looked great...
He's full of ****. And if you believe him you need to learn about performance parts. 15-20 hp from a good tune....sure. When he said "100hp" I would have been rolling on the floor laughing.