Is the flu contagious before symptoms appear? & will flu shot have some protection against other strains even though it's not a good match this year?

Yes: You are contagious before you have symptmoms of the flu and this is the case with many viral infections. This is why they spread so easily. Once you get symptoms of the flu most people feel so badly they know and others know to stay away. Once you have been exposed the flu shot will not prevent as you need close to two weeks to prime your system. It is only about 25% effective this year.