Question:

Was there a ritual (cleansing, education, ceremony, etc.) that a Levite must go through before he became the high priest?

Answer:

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.