[eVitO]

I can answer some of your questions. Your first one with weight of the wheel: wheels weight is UNsprung weight, which makes a huge difference in total performance of the car with a couple pounds of difference in either direction.

I don't think wheel weight affects ride quality, but I may be completely wrong with that one.

Moving from 17" to 19" would mean that you're getting a tire w/ a smaller sidewall, which is what absorbs a lot of energy from the bumps on the road. Which takes me to your next question: all of those tire sizes decrease in sidewall size, which is what affects ride stiffness or harshness. I don't think tire width has anything to do with it, just the sidewall width. Maybe some tire guru can expand on that and I may be wrong with that too, but I don't think tire width makes a difference.