What birds and model incubator do you have?
Do you know what "market" you are planning to sell into? Hatching chicks is the easy part, marketing and selling can be the part that makes most people rethink whether they want to do this. Some people are natural "sellers" and their enthusiasm makes the marketing easy.
There is a growing interest in keeping laying chickens in the backyard (obviously, you know that if you've been on this site for long). Trying to sell anything that does not play into that market is a very limited market, but if you can produce female chicks of good laying breeds, you will likely sell all you can hatch. Unsexable chicks, bantams, show birds - those are neat, but the demand is very low compared to sexlinks or autosexing breeds of layers (Rhodebars, Legbars, etc).
Some things to think about:
1. what will you do with the male chicks? (don't say you'll sell those too, I can tell you you can't give them away, unless you kill and freeze them for reptile keepers)
2. do you like dealing with people, and teaching them about chickens? (I often spend an hour or more explaining the basics to people when they buy 4 chicks - not a business plan that scales well)
3. what is your policy when someone is unhappy? what if they get a male by mistake, will you replace it with pullet the same age?