Was there a ritual (cleansing, education, ceremony, etc.) that a Levite must go through before he became the high priest?
Among the Levites, only descendants of Aaron could become priests or high priests. Other Levites served the Lord but in different functions. The consecration of a Levite before his service is covered in Numbers 8. The consecration of priests and the high priest is covered in Exodus 28-29 and Leviticus 8.