Possibly very few. In his best-selling book "The Rise of Christianity," author, and sociologist Rodney Stark, who has written over 50 books, estimates that in 100 A.D., there were only about 7,530 Christians in the entire world. Conservative Christian Bible scholar N.T. Wright has said that in the first century A.D., there were not enough Christians "to start a riot in a small village."
Rodney Stark also uses evidence from experts in papyrology, and archaeology, to show that there were very few Christians in the world in the first century A.D.
If Jesus did not perform any miracles, including many miracles "throughout all of Syria" as the New Testament claims, that might partly explain why there were so few Christians in the world in the first century A.D. since people who lived in Jerusalem, and Syria, could easily have checked out claims of miracles for themselves.
If Jesus actually did perform many miracles for three years, I assume that he would have easily become a media sensation, and would have attracted the attention of the governments of Jerusalem, and Syria.