Before looking for property for your homestead, you should have an idea of what your homestead will produce. this will help determine the requirements that your land must meet, and what will be required from you to make the land suitable. Once you have that figured out you can begin your search for the perfect property. Note: your plans will surely change at some point to some degree so try not to lock yourself into anything that may hinder you in the future. If you already have property, great! You have completed the most difficult yet important part of the process!
Not only should you consider site planning, you also need to consider local laws and regulations. Some things you may want to do may not be legal in your area, or require certain permits such as selling eggs, processing meat, selling meat, etc. Land improvements such as structures, well, septic, etc may need permits depending on your area.
The quickest way to find out the specific requirements for your area is to contact the building inspector for your locality directly. Their direct contact information is usually listed on the government website, which can be found with a quick Google search. Simply search for: "your area" building inspector.
If commerce is part of your plan, you should contact your local Chamber of Commerce for guidance on licensing requirements, and other available resources. Members of the Chamber of Commerce are not elected, they actually have to pay a membership - so they are there to help. They are probably the most helpful of any government agency, especially since they're not looking at which pocket your wallet is in. They may prove to be one of your most valuable resources of information and connections.
We really need some experts to chime in on this subject. Homestead planning is EXTREMELY in depth due to the large variance of activities that happen on a homestead. These include various livestock, each with different needs, gardening and farming, which can require multiple locations and specific requirements such as geography (placement with sun, on hills, etc), and available resources (water, soil, etc), and sometimes can include multiple dwellings and even habitat preservation sites. One major consideration should be security: on a homestead, we have tangible investments that must be protected. The experts on these subjects have spent an incredible amount of time researching specifics such as security, garden zones and applicability, pretty much every aspect of homesteading. I will be posting links to that info as I have time, feel free to jump in and post some of your own.
If you have any knowledge, resources, or experience, please post it for others who may need that information.
Happy Homesteading!