Christians, do you that Christianity first became a movment, you had to convert to Judiaism before you could worship Joshua?

You seem to be confusing the concept of being a proselyte, or Gentile convert to Judaism, with truly becoming a Christian. It's true that over the years, many Gentiles became Jews (Ruth, of Moab; Uriah the Hittite; perhaps Ittai the Gittite (from Gath, a Philistine city). During Esther's reign as queen of the Persian empire, according to chapter 8 or 9, many people of the Persian empire became Jews. Even Nicolas, from Antioch, was a proselyte from Antioch.

But there were different levels of proselytes. Some were called "righteous Gentiles", and others were "proselytes of the gate". They followed the Jewish faith but were never circumcised. Some Gentiles did become circumcised and were considered authorized to take part in the Jewish ceremonies, etc.

What settled the question of "Do Gentiles have to follow the Law?" was settled once and for all in Acts 15. The only things Gentile believers were asked to do were listed there. No, nobody has to become a Jew in order to become a Christian.