In general- they will want to be sure that you DO intend to "engage in the business" of buying and selling guns for a livelihood- and not for your personal use. And that you have covered local legalities- zoning, licensing, etc. Then they talk to you.
You are about to get a good, in depth lesson in the legalities of being a FFL. My honest suggestion- have a pot of coffee for the two of you, have a couple of legal pads and a couple of those pens with a LOT of ink- and start taking notes. The lesson is free, and stuff you are going to need to know to stay on the good side of the ATF.