Check with the town clerk where you live to see if the town and zoning codes allow for such a business. Also check with the town council or board of trustees, building inspector, planning and zoning boards to see if they will approve your business. The town clerk will help you navigate this. Make sure to communicate will all of these local entities because, incredulously, they often do not communicate with each other very well. If they will not approve the set up you propose there is really nothing you can do but look into renting a kitchen space.
Do not skip this step!!
If you do, it's very possible that you will spend a bunch of money setting up your kitchen only to have a neighbor inform the town government and then get you shut down.
This, above, is never allowed anywhere. If you wash your hands where you dump your waste and mop water, you can contaminate your hands with dirt and bacteria etc from the residual gunk in the mop sink.
Here are some other basics that apply in just about every state:
You need a triple sink with indirect drains. Indirect drains are very important. You also need a mop sink, hand sink and a separate bathroom that is separately vented. Sometimes a tub in the bathroom can service as a mop sink. If you have a commercial dish washer, you will only need a double sink, but still with an indirect drain.
You will need to purchase commercial grade appliances.
All light fixtures must have protective coverings of some sort so that if a bulb breaks, glass and other particles will not contaminate the food you are producing.
You will need adequate ventilation and a fire suppression system that is approved by your local fire inspector.
Your license fee will depend on whether you have city water/sewer or a well/septic system. The fee for well/septic is more expensive due to the need for testing and monitoring of water quality and the working state of your septic system.
If you are baking to package and sell at farm markets and retail outlets, you will need to be approved by the state department of agriculture. You may find the Dept of Ag a little more helpful. The Dept of Ag usually supervises farm markets, but each market has its own manager and board of directors. Make sure to communicate with these boards before you sink a lot of money into your business. Farm market boards can be ridiculously picky about what you can sell, protective of the vendors that already participate, and have romantic notions about what the words "locally grown and produced" mean. These boards are also unusually blind to what will help their markets grow and thrive.
Good luck, but take some honest advice here. Look into renting time in an already approved kitchen and write a business plan (INCLUDING ALL THE FINANCIALS) before you sink a bunch of money into your scheme. This will show you whether you can actually make money with what you propose and also whether you are cut out for this type of business. It can be great on a small scale, but a burn out when your business grows. Plan ahead for your success and see if you really like doing it in a big way.
Many home bakers are encouraged to open bakery businesses by their friends only to find they do not have the operational aptitude for baking on a larger scale and dealing with the pesky management of capricious clients and suppliers, inventory and cash flow statements.