回复：问个independent contractor (self-employed person)问题

w-9 is to get your leagal tax id and address...

FICA for everyone is 12.8% and 2.9% respectively currently, but employee only pays half while employer pays another half. Since you are a contractor, they will not pay the matching portion (50%), comparing with employee, you look like paying double.

For how to reduce taxes, you'll probably need to ask tax experts or your CPA for advices.