Rare. But it can happen easily depending on the type of strep. Some are more virulent.
It depends. There are multiple kinds of staphylococcal bacteria strains. Whether a person develops sepsis is dependent on the type of staph strain, as well as the overall condition of the patient. For example, even a "weak" staph strain can cause sepsis in somebody whose immune system is weak. We all are exposed to staph virtually every day. It is impossible to quote you a percentage for your question.