I can't speak for other states,but Texas only requires a state tax number,and the city requires you file a business name for the most part.
There are many "I BUY GOLD" businesses here.They even open them in small towns with population's of under 10,000 people.
When the supply dries up they move on to the next town.I have visited several of them and find that they only offer about 30% of spot price,if that.
They will set up a couple of display cases with low grade,but attractive gold plated jewelery and point to the prices in order to buy k gold for such a small price.They will even close up and move out on December 31 to avoid janurary 1 inventory tax. So ,I think it's safe to say you could set up a ,I buy gold ,in most states in much the same, or close to the same way.