Not a manufacturer, but will give this a try-
ATF- they are looking to see if you are legit. do you have a premises? Do you have the OTHER legal things to do business (business license, zoned for business, sales tax ID number, etc) Do you have secure storage for firearms? (Could be a lock on the door, safe, locking cabinet, lockable room) Do you understand the limitations of your license, and paperwork? As a maker, you will have Fed Excise tax to pay- are you set up for accounting for that?
As far as OSHA- has nothing to do with ATF. How many employees do you have? Fewer than 3, you are not subject to OSHA regs. If you have more than 3, send me an instant message, and I can help guide you thru some of what you need for 30 CFR 1910, standards for General Industry.
With inspector it is OK to ask questons of him- part of the purpose of visit is teaching. You can offer him a cup of coffee (he may or may not accept) DO NOT offer him dinner for 2 at Ruth's Chris.