Pro covered the glass part so here my opinion on the sanding/grinding scratches......i would sand down to the scratches then cover all the scratched areas with a "skim" coat of filler or spot putty to fill all the deep scratches.

Then use a good quality "filling" type of primer made by 3M and that should take care of most the scratches.

And i feel your pain bud i had a 66 gto that looked like someone used 36 grit on a grinder to remove the paint......it was a scary sight and a pain in the A$$ to smooth.

good luck