Our farm has been transitioning from cottage industry / farmers market sales to int
erstate commerce over the last couple of years. What I can tell you is that state laws differ greatly, but your county extension office can either answer your questions or tell you who can. For federal laws, they can be helpful but often fall far short of being able to figure it out.
The FDA does have a hand in your business the moment you offer to sell across state lines.
http://www.fda.gov/Food/GuidanceRegulation/FSMA/ucm334114.htm
I know from experience that if you do sell across state lines, they will find you, they will send you a nasty gram, they will tell you about the huge fines and even potential jail time. Oh, and they won't tell you about the exemptions that the FDA has for small farms.
http://www.fda.gov/downloads/Food/GuidanceRegulation/FSMA/UCM472499.pdf
Chances are, you stopped the flow chart at 25K in total sales. Don't because that is total sales, not profit. If at all successful, you will slam in to that figure soon enough and still be dirt poor. The next exemption is partial. It hits at 500K and below, but most of your sales must be to the consumer who will be eating it (not a business) or fairly local restaurants or retail food establishments.
Essentially, by the time you cross 25K for three years, you already need a plan to be compliant. Its not just being complaint with paper work. If you read the rules, you will quickly learn that there are federal laws for just about every thing. Where you germinate, the green house, any pets or farm animals, any building you might use, and so on.
If you read the rules in the first link, you will understand what a pain in the rear it could be. A corn farmer who is visited by deer would have to flag everywhere a deer pooped. Most I know do not walk threw each row every morning so how the hell would they know where the deer pooped?