I don't have a whole lot to add to the discussion of what the law says (Bluemoon420 pretty well summed it up), just this. The Michigan Court of Appeals has made it very clear that there is no minimum size needed to be commercial. [T]here is no minimum level of sales that must be reached before the RTFA [right to farm act] is applicable. Charter Tp. of Shelby v. Papesh, 267 Mich.App. 92, 101, 704 N.W.2d 92, 99 (2005)(the case was actually about chickens too). However, if your hens lay 4 dozen eggs a day and you sell (or try to sell) one dozen a week while using the rest you might not win in court because the selling looks like just a cover. If you sell half of your eggs you are probably good.
I am allergic to eggs so my farming does not involve chickens, which is too bad because they are one of the easiest and most affordable animals to start with.
Just because you are right on the law does not mean it will be easy. My Michigan right to farm story. I am not a lawyer yet (I am taking the bar exam for the first time later this month) but I did well in law school and I have extensively researched this issue so I figured it would be pretty easy to deal with the city. We are growing vegetables to sell and had an issue with the city's plant/mowing ordinance. During the hearing before the city appeal board I not only cited right to farm, but read the relevant portions of the law and the GAAMPs. The city attorney was quite possibly the rudest person I have ever encountered, laughing every time I discussed the law in my argument. He stood up and basically said that the law didn't say any of what I had read (he also misstated my argument even after I corrected him), he did not cite the law to support his argument, he did not give any backing for his bold statement that right to farm does not apply in the city and he made very demeaning comments about my arguments and about our farming operation. The board voted with him unanimously and without discussion.
The moral of the story. The Michigan Court of Appeals has almost always sided with the farmer in right to farm cases, but unless you are prepared to go that far do not count on getting the city, township, or village to let you do what you have a legal right to do. Also, expect that you may have to deal with belittling and demeaning behavior on the part of the municipality.
That being said, good luck and I hope no one else has to deal with this kind of ridiculousness. Unfortunately our Circuit Court judge does not like unrepresented people in his court so we will have to wait until I am a lawyer to pursue our matter further (If anyone needs a letter from an attorney to a municipality I am sure I will be able to beat the prices that dw_bubba was given once I am actually an attorney).
If you cannot afford an attorney, see if you can find someone in your local Extension office or Michigan Farm Bureau who knows the law and can write a letter, it may help against an ignorant official so long as they are not trying to lie about the law like ours are.