There were a few factors that went into the wheel and tire selection.
Since this is my daily driver, I did not want a vehicle that I would continually have to change tires due to weather. That said, I needed all-seasons and they did not offer any larger than 18".
The other dominant reason for the wheel size is because I am really trying to make my car look more "classic" than modern. No 20-inch wheels in 1967 and none of the bling-bling looking garbage during the 60s either. I chose 17s because they looked like wheels on an older mustang... including the '68 in Bullitt. If you'll look again, you'll notice that the wheels are almost identical to McQueen's ride... except they are black instead of anthracite.
A lot of people have urged me to get bigger wheels, tires, etc... but that is probably the one area I am most happy with my vehicle and least likely to change. The tires are good year-round... and the wheels are classic instead of "gangsta." I think 20-inch wheels look fine on new mustangs but I would not put them on mine. It's a personal taste thing.
As for the headlights... I got them for the unique look. As I said in a previous post, I am kind of going for an older-looking mustang with some Eleanor-type touches. I am currently very satisfied with the way things have turned out so far. The lights work great... and I like the Halos when the park lights are engaged.
The bad thing is that my car has had to endure some really ****ty weather since I got it. I am so done with this snow garbage and am anxious for warmer weather so my vehicle can actually look decent without the salt and snow residue.