There are specific repair materials for plastic bumpers (not bondo or fiberglass), there are some DIY kits with colored repair material. I would start looking at those if you are diy-er.
TPMS74 is the motorcraft part number and are the correct ones... The full kit M-1180-433MHZ2 from ford performance is also the correct kit. Others may work (not sure), but I know that these two options for sure work.
I am running 235 wide winter tires on my S550, though not a PP car (18x8)... you will need 19 inch for PP car. If I was driving the PP S650 car in the winter (which I don't), I would get a set of 19x9 square (eco PP takeoffs) and run 255/40-19 winter tires.
They do say it fits... however that was said for the ones I had originally purchased early on with mine... at the time, many vendors had it wrong. I do know that the ford performance kit I listed does for sure work.
I fell in love with the royal crimson... bought the car on a whim, I was at the dealer getting airbag recall replacement on the S197 Mustang and was looking around the lot, saw that color and it was all over, never drove the old mustang again.
Much nicer drive than with the original frame... it rode like a buck board wagon. It had lots of chassis twist trying to put down the HP... now just grip and go! You building frame frome scratch, or have something to start with?
Did the check for the last two Mustangs... I think the look goes from surprise to disappointment that they can't "sell" you some financing. Years ago, I paid for a car with cash... the finance guy was downright angry (that he had to count it?).
How did we go from fender holes to checks... lol...