Well Lin, this is just my opinion, but from the cars I have torn apart to parade rest and back I think I would put the windshield in first because then you won't have to be leaning over in-thru and around the doors while trying to install it. But then every car is different and sometimes I just need to be there to see what feels right at the time. I'm not sure which items you mean by 'aluminium sills'. If you just mean the cover plates, I usually do them last. But then hoping that the doors are adjusted correctly and have enough room. Good Luck.