+1 informative, +1 helpful, ++? generally spot on
Also +1 informative (again) because I didn't know the details of the US distribution grid. I only have experience with our 240V system here in South Africa.
I did know about the 120V centre-tapped system, but we don't use that here [SA], or in Zimbabwe (where I'm from), or in UK (where I lived for a long time.) -- these countries all use 240V.
Good luck with the whole upgrade!