Molting supposedly starts around the head and neck. In some of mine it did. Lots of good pics on here of molting. Mine didn't do it all at the same time either.
They feel varying degrees of lousy when they are molting. I've read that hens who ordinarily love to be cuddled and held didn't want to be touched when molting. I've read of poor appetite, some weight loss, even some diarrhea. I had one who had a heavy molt who seemed to stay off a bit by herself though she still hung around fairly close to the flock. She wasn't as interested in treats as usual. She is now fully recovered and back to her usual feisty self -- and is really beautiful, such glossy new-looking feathers.
I just got them eating BOSS so that's a handy protein treat. Before, I did do a little protein supplementing, but not a lot.