How do I become a Proprietary Trader?

How high/low is the demand for this career in Manhattan (Wall Street) and what is the average salary in Manhattan, this is one of my serious interests for a career, I know I want to do something in business. Also, my uncle said to get a dual college degree in business and law, but why get a law degree? I won't be able to become a lawyer without numerous more years than just a bachelor's degree. Thanks and please answer both questions if you can.