You are correct in that the business side is the most difficult. Getting you FFL is a rather simple process. Getting set up with dealers is when the work really starts. Every vendor will require at a minimum: a copy of your FFL, a copy of your business license and a copy of your sales tax permit. All of this will likely be needed to get a bank account setup too. You will also need a Employeer Identification Number, EIN, regardless of whether you have employees or not. Once you get your FFL, as well as these other documents, scan them and make a folder on your PC to hold them. Then when you need to send a vendor your information you will have it all in one place and ready to go. DO NOT sign your original FFL. Make a copy and sign ONLY that copy. Your original FFL, unsigned, is considered a 'certified copy' and the original document.
Something you may or may not know is that your IOI does more than deal with firearms dealers. My IOI also does inspections on coal mines, rock quarries, construction sites and places where explosives are used, stored and tested.
So far my experence with the, BATFE, has been nothing but pleasant and helpful.