You'll want to get a Business License first, and you'll want to check to see if there are any location or other restrictions on that type of business. Look at the way other gold dealers are set up and perhaps you might follow their example. Good Luck on your new business.
You should hire a business lawyer experienced in the retail commodities business. Buying gold from people is probably regulated by the State of Massachusetts and may be regulated by some branch of the Federal Government, e.g., the SEC. This is not something you are likely to discover on your own. Nor are you likely to get the answer on an internet site unless that one lawyer in a 100 is reading your posting.
As Mr. Potter suggests, you should get a business license in the area in which you establish your business, e.g., Boston. You should hire a competent CPA to help you establish your business in the appropriate format, probably an "S" or "C" corporation.