Aside from the narrator, who else will likely become a major character in the story? What characteristics are reveled about him in first chapter?

Certainly Phineas will be a central character. He is Gene's character foil. Where Gene is conservative and introverted, Phineas is extroverted and charming. "Finny" could get away with anything at school. Frequently teachers would merely smile and shake their heads good heartedly at infractions that would have landed any other boy in trouble. Finny is handsome, strong, athletic...He is everything that Gene wants to be. Both Gene and finny are characters that attract each other and polarize each other at the same time.