If I'm understanding you correctly, what you are talking about is NOT dealing in firearms, but barter. Accepting payment for services in something other than cash.
It just happens that you are willing to accept (some) guns as payment. You could accept eggs, or some other service from the chicken ranch...
I think the only thing you should have to worry about (provided this is not the main way you run your business) is ensuring the tax man(at all levels) gets their share of the "value". If its on the books, taxes must be paid, and regardless of what you accept, they only accept cash.
Lots of people do lots of things for friends, off the books, and barter happens all the time. But, if you are accepting barter as a business practice, that's "on the books" and values must be assigned, records kept, and taxes paid.
Don't think you need to worry about an FFL license, small number, for your personal use seldom falls into the "engaged in the business" category. There is a difference between accepting property (even guns) as payment for a debt, and dealing in firearms. You can even sell the guns you accept, at some point, just as you can any other in your personal collection.
But, obtaining guns, and then selling them, as a means of earning income, IS engaging in the business, and needs a license to be legal.
I'm not a lawyer, this is just my common sense advice, and worth what you paid for it. You should check with a lawyer familiar with your state and local business laws, as well as firearms laws. You may be fine on one side, and have hoops to jump through, or even be prohibited, on the other. I don't know. Find out, so you don't get into trouble.