Greetings! This has been talked about quite a bit here- search the FFL topic for threads that have kicked this around.
In a nutshell, there are 2 licenses most commonly sought- an 01 Dealer, and an 03 Collector of Curio & Relics. For an 01, you must intend to "engage in the business" of buying, selling or repairing guns. You CANNOT get an 01 FFL for personal use.
An 03 is good, but only covers guns that are 50 yrs old or older, except for some newer guns that have been designated collector's items.
For an 01, you must be in compliance with state and local laws- including things like ZONING, and having a business license. Required before ATF will issue permit. Storefront is NOT required, but you must have designated premises and hours of operation.