1) What is difference between Rehbar and mujhtahid? Ayatollah khamenei is our rehbar and few people follow ayatollah sistani and few other mujhtahid for taqleed.
2) And is it mandetory do taqleed?

1) Mujtahid is for Taqleed in Fiqhi matters, and Rehbar is leader in social and political affairs.
2)Either a person can be a mujtahid themselves or follow a mujtahid in order to know the rulings of shariah which are necessary for daily life.