I don't want to give specifics since I only know what's available in my area. Most communities, if not all, have free clinics available for immunization. There is recommended schedule. Every year as new vaccines are added and combination vaccines are created, the schedule changes somewhat. Yes, there are recommended schedules.
Every pediatrician is aware of the schedules.
Some vaccinations require booster shots and, in fact, most vaccinations are not a one-time vaccination. The reason behind booster shots is especially for vaccinations administered to infants and young children, their immune system has not been fully developed at time of immunization, so that a booster dose boosts the immune system to produce a more powerful reaction to the offending organism. Someone may ask, well why don't we wait until children's immune systems are more fully developed. For the immunizations that we administer at a young age, they are susceptible and sometimes most susceptible at that age to the diseases we are trying to immunize against. Our philosophy is that if we try to protect them as much as possible, better to do it then than wait until it's going to be the most effective as far as developing an immune response.