Depends on the scale you mean. Do you mean just sell some from your backyard flock? You should be able to just declare miscellaneous income on your tax return for that. If you mean starting a proper business, you'd want to talk to an accountant or the like.
Tips:
Do you have breeders already or are you going to choose fresh? If you're choosing, do lots of searching on FB farm and poultry sales groups and see what sells, and what sells fast. Try to raise that type.
If you're going to sell out of state or ship hatching eggs, enroll in NPIP and get your flock tested. Also, you could talk to your county or state extension agent to see if there is any other certification or testing you need in your area, since you don't list it. Some areas are stricter than others.
Have a plan for those that don't sell and leftover males, especially if you'll be breeding ones that can be sexed at hatch. Nobody wants males. Well, very few do.
Make sure you can afford to feed your breeders well and that you can feed any unsold chicks, too.