A plucky young Canadian editor is mounting what might be considered the ultimate Quixotic challenge of the book world: building, opening, and running a major new independent bookstore in the heart of New York City. “She knows that the city’s independent booksellers have been dying off, squeezed out by skyrocketing rents and stiff price competition from large chains, such as Barnes and Noble, which gives no quarter in the town where it began.” But Sarah McNally comes from a family of experienced indie booksellers, and her family is throwing its considerable financial weight behind her new two-level, 7000-square-foot store in downtown Manhattan. The store opens this week with a staff of two dozen, and will stock 40,000 titles.