Good news / bad news:
Bad first:
Mr. Koginam & Mr. Keegan give very good advice, I think. Good small businesspeople are very rare, and very busy.
This is a business first. you must know how to operate a business. This will not happen by accident.
That means (at MINIMUM): building a capital / debt structure, obtaining adequate working capital (two years), location, real estate, maintenance, utilities, taxes (personal, property, business) & insurance, licenses (FFL, business), loss provisions, payroll if you're lucky enough to afford employees, inventory, record keeping, tools and equipment. What happens if you get hurt or sick and cannot work? This is only a partial list.
More than 90% of startup businesses fail, nearly all within the first year.
Very few of the gunsmiths I've known of actually make a good living.
Most people get an attack of common sense and decide it's a better hobby.
Good news:
It can be done succsessfully. Messrs. Keegan & Koginam demonstrate this.
It probably is a very satisfying profession, once mastered and established. Learn to be a machinist and welder if you want to specialize later on.
One good book is "Pistolsmithing" by George Nonte. Applies mainly to handguns, but very strong on the principles which apply to anything. Long out of print, but usually available on Amazon.