A whole-system generator would likely be connected to your electrical system at the main service entrance at the meter pole. Check the requirements of your local power supplier for details on power transfer switching. Small, portable generators can be used to supply power to individual appliances simply by plugging them into the generator. Generators require about 2 hp engine capacity for each 1,000 watts of generator output. Your main concern will be to provide capacity for starting motors.
Motors require three to five times more electrical current to start than to run.
Estimate power requirements from electric equipment nameplates if possible. As a guide, electric motors require roughly 4000 watts to start and 1000 watts to run for each horse power of output. Electric heating devices would drive the requirement much higher. Typical farm demand could easily be 15,000 watts or more. In some cases the generator capacity may not be sufficient to run all essential appliances simultaneously.