1) They lose their feathers and regrow nice new feathers once a year after the first year of life. The young chick goes through 3 partial molts in their first year of life.
2) It really depends. I've had a hen molt very slowly, and a hen that lost the majority of her feathers in a week.
3) Again, depends. Usually fall, but I have a hen that started molting 2 weeks ago.
4) Not all at the exact same time, but in the same season it would be more likely to happen.
5) You would switch them from layer feed to grower feed. I never take mine off grower, but it's best to give them lots of protein during the molting process. I would leave them alone. Don't pick them up - this is really uncomfortable for them.
Hope that helps.