i work in the glass industry. personally, i would remove the front sheild myself, correct any rusting conditions, the have a mobile glass company ( most all are, if you ask) come out and install the new one.
second, the rest of the glass in the car is all tempered, light sratches can be removed assuming you can't feel them with your fingernail. if you can, then most likely when you start to polish the glass, small fragments of glass debre will come out of the scratch, mix with the polishing compound, and start scratching the surface of the glass, leaving you with more of a mess than you started with.