the PC isnt going to do anything for you on the glass as glass is 10 times harder than paint! all you are going to do is fill in the chips and remove the hazy from it kind of like oxidizing paint. You can safely use a sealant on the glass as well, its not going to do any harm, and it will act like rain-x and repel rain/water. Claying the glass will improve clarity AND reveal more chips as it will remove the dirt that is currently "filling in" the smaller chips!
best bet is to just get it replaced. In fact, most windshields are in the $200 range, so thats just about $50-60 more than the PC, and less than the PC and all the pads and products you will need to buy. If you were going to be polishing and detailing multiple cars, then I would recommend the PC route, but if its just your car and youre not going to polish the car, then you are wasting your time/money.
Get a new windshield.