As the man said- if you intend to "engage in the business" of buying and selling guns, you need an 01 FFL. Otherwise you get to meet the folks in cheap suits with bulges.
As far as light rust- CLP or any good light oil- I like KROIL. Wet it, let soak for an hour. Rather than steel wool, stop in housewares section at the grocery, and get a Chore Boy COPPER pot scrubber pad. Copper is softer than steel, and less insulting to bluing. Wet the pad with more oil, rub gently. Metal will start to look coppery- that's OK. Take a clean soft cloth, bit more oil, rub. Thin trace of copper and rust comes off. Switch to clean spots on the cloth as needed.