These are just some expenses I'm throwing out there for your consideration:
Feed for breeding birds to have the best chance at viable eggs for reproduction.
Space requirements for numerous pens of breeder birds.
Grow out space requirements for "kept back" breeding birds that you are considering keeping.
Health requirements for your state/shipping codes.
Vaccinations should you choose to offer vaccination of chicks.
Heating requirements for brooders.
Incubation requirements, heat, humidity, etc. Electricity is going to play a HUGE part in expenses, especially considering if a power outage happens, you lose that "crop" of chicks and have to start from scratch.
That's not even counting the amount of time and effort you will need to put into building your reputation as a reputable hatchery that has excellent customer service.
But then again, I'm basing this on my assumption that you are hoping this will be your only means of income? Is that assumption correct or are you going to have a second income to help supplement?