1. It won't hurt the plant.. The general rule of "blue for veg and red for flower" is to save money. The plant absorbs both ranges of spectrum in both stages of its life.
2. Autos are like photos. It's different from strain to strain and seed to seed. However, if it's the "Grandaddy Banner" from your diary, then the breeder says 8 - 9 weeks of flower time.
3. Yield depends on a lot of things.. how well you take care of your plant and genetics are primary factors. I've seen people outdo breeders expectations by miles, and other people only get 10% of the expected yield. General rule when expecting a yield, is the number that the breeder gives, is absolute best outcome, no fuckups, perfect condition. So expect less than what they say, both with autos and photos.
I hope you get great results with your first auto grow. ^_^