I do sell at farmer's markets. Poultry does not fall under USDA inspection, except for processors of over 19,999 birds per year. So therefore, poultry and rabbits fall under State inspection, which means it's entirely different in every single state. Some states are very accepting of small producers, others are not.
In my state to sell off my premises (such as at a market), I must either get a permit for my farm (requires inspection and some production facility not inside your domestic kitchen) or I must go through a State inspected processor (of which there are only like 4 in the whole state who'll even return your phone call). It does work out as I take pre-orders for a set processing date where everyone comes to the farm to pick their birds up, which are bagged and chilled only through a processor. In every state, freezing, repackaging, quartering, etc. is considered 'processing' which you cannot do yourself.
I think the advice you got from your extension office sounds great. Just be aware, you always need to let them know what you are doing, and likely they'll assing a "food safety officer" to your farm. How you store, refrigerate, package, etc. the birds if you process them is very critical and has to be done "by the book"... whatever your State book says needs to be done.
I hope you enjoy your adventure. I too sell at $3.50 per pound for whole birds only. They are pasture raised and given certified vegetarian feed. I no longer do Cornish crosses, though. I'm working on my own breeding and also am very fond of Freedom Rangers, which you should check out if you seriously get into pastured poultry.
Oh, finally, do not even consider attempting this without getting yourself a business license and insurance. I would not get a rider to your home owner's policy, unless it's specficially a farm policy rider. It's literally cheap insurance... and whenever dealing with food, your liability is immense. No 'hobby' is worth losing your home and life savings over.