The regular cohein had 4 articles of clothing: a tunic, pants, a hat and a belt. The cohein gadol had 4 more: the breastplate, the eiphode, the cloak and the tziz.

The cohein gadol can only use the urim vtumim to ask questions for a king or the sanhedrin or for someone questioning on behalf of the public.

Yuma 8:1

On Yom Kippur you cannot eat, drink, wash your body, anoint yourself, wear leather shoes and have marital relations. R’ Eliezer says a king and a bride can wash their face and a new mother can wear shoes. The Chachamim disagree.