If you are getting an FFL (1-3) to make money, forget it. Lets say you want that second income to be approx $30,000 a year. To make that amount of money at lets say the common 10%. You would have to gross minimum $300,000 (this does not include overhead or other costs that will eat at that 10%, down to like 4%). Most shops have to run a 35%-65% profit margine just to stay afloat. Adjust the numbers as you see fit.
I have found that just selling guns and products truly does not add up to the income you desire. You will need to add services such as gunsmithing, bluing and other finishes. But, REAL gunsmithing is where it is truly at. I say real because there are so many folks out there that call themselves a gunsmith because they can tear down their own guns & put them back together with only a few parts left over, that they feel they are qualified to do real gunsmithing.
You will also need to add services such as firearm & CCW training either done by yourself (You need to be certified in most states) or have the training contracted in. The other real money maker is a shooting range, there are unbelievable profits in that aspect, even though costs are very high as well.
You will then need VOLUMN's of those services. Selling ammo onesey - twosey will actually cost you rather than make you money as people can get their own ammo sent to them (some states do not allow home delivery of ammo). This is the same for reloading, most shops do not even have or minimally have a reloading section of Powder-primers-bullets-cases because the potential customer can get it all w/o a middleman. Also, you cannot ever stock enough items to make everyone happy. I have found I make about 5-9 times the money doing gunsmithing than I do any sales, sales are mostly done as a courtesy to the customer.
Basement dealers think because they made $40 on a $400 gun sale is good money. In the end you will find out just how much you are paying for that $40 if you follow the Fed, State and local laws.
If you applied for the license just to get good deals for yourself and a couple friends, the reform of BATFE is soon to stop that as well as the occasional basement dealer as the new reform will state a minimum quantity and or dollar amount per year to retain your 01/02 license. The reform I think is currently being tossed around in DC.
If you just want guns cheaply and sent direct to you, get a 03 C&R license. It does not allow you to run a business, but you can get some really cool guns and it also allows you discounts at many places like Midway, Sarco and Numrich to name but a few. Since it is NOT a business (it is a collectors license), when it comes up for re-license and you decline, you do not have to send in your records of incoming/disposition of the guns. The BATFE have the right to review the records for up to 7 years after end of your license.
ALL of this is just IMHO - please feel free to rip my opinion apart as I am sure will happen