Obviously you will grow the plants that you want to eat, but this can be a chicken and egg situation as until you have tasted something, how would you know whether you like it as many of the plants available to choose from may not have crossed your palate? You can very quickly have 20 species growing and some gardens will have more than 200. It can be helpful to visit a Forest Garden and taste a few things before you buy. Many people build the basis of the planting in their Forest Garden on the plants they are familiar with and then branch out to include other less known species.
Choose species that will suit your local climate, soil type and aspect. For instance fruit trees that do well in the Southeast of the country may struggle to perform well on a West coast location due to very different levels of rainfall.