I'm a licensed, trained (Colorado School of Trades) gunsmith who's been in business for the last 29 years. Mostly retired now. Lots of things involved if you're going to do it proper and legal; if not, you're headed for trouble. First you need an FFL. Period. Second, if you're going to be buying components and fitting them into firearms for sale, according to the last time I talked to my local ATF agent, you need a "manufacturers" license"... assembling parts is now considered manufacturing a firearm, and there's an excise tax per firearm associated with that. Unless that's been changed, so you would need to check with your local ATF agent for their interpretation of the law. Also don't forget you're going to need a buttload of liability insurance. One mishap, your fault or not, and you're open for a possible big-time lawsuit. Lawyers don't care if you're guilty or innocent, your fault or not; you will be paying for one, and you might not want the cheapest one around, so good insurance is a must. I carried one milliion dollars; for that kind of money the insurance company will help with the lawyer...
There is a market for the work, and you might be able to do mostly 1911/2011 work, but until you get your guns out there doing well, not many folks are going to give you big bucks to make a firearm for them. AR's are hard to make much money on as the parts are cheap and readily available to nearly anyone, and everyone and their brother seem to be able to put one together in a few hours that will shoot MOA.
So what you're left with is making a small profit on parts (which you want to get at dealer price) and labor. Frankly, there's not much margin in either one unless you have one of the big names/reputations as mentioned in an earlier post. Where you make any real money is in the margins on equipment, for the most part... magazines, ammo, holsters, bags.. in other words, the stuff you have in the store to support your gunsmith hobby.
So you want to get in? Can you go to one of the colleges or schools that offer gunsmithing? Can you be an apprentice to someone with a good reputation in your area? Take a correspondence course? Get a job in a local gun store? None of these are absolutely necessary, but you'll do better to look at those kinds of opportunities probably than to hang out your shingle and hope to make it to the big time. I wish you well, I have all the business I want, but it's taken me a long time to get here. Good luck, look into it carefully, and be aware of all legal and financial obligations. Business savvy is very important here. Ask around... talk to gun business owners... and here's wishing you all the best as you begin this journey!