why is the little chinese seamstress the most important character among all?

The unnamed narrator and protagonist of the novel is a thoughtful, intellectual 17-year-old who is sent to the countryside for re-education during China's Cultural Revolution. He lives there with his best friend Luo. Unlike the narrator, Luo is outgoing and theatrical, and is less pensive. He falls in love with the Little Seamstress but never acts on it, and is transformed by the power of literature. Please check this out for details relating to your plot points an climax:

http://www.gradesaver.com/balzac-and-the-little-chinese-seamstress/study-guide/summary