There is no right or wrong number of Goals to include in a Dashboard. If your Goals have numerous Indicators, you might want to include only 1-3 Goals on a Dashboard. If your Goals have 1-3 Indicators, you might want to include upwards of 5 Goals on a Dashboard.
Each Goals Dashboard should have an intended audience and purpose. What are you hoping to learn? What is the story of impact you are trying to tell by sharing this Goals Dashboard? You can set up multiple Goals Dashboards to help organize your Goals for different programs, departments, initiatives, etc.