1 & 3) In the Giver leadership was totalitarian. Society was run the council headed by the Chief Elder. The council dictated the rules of society and because the members were brought up to want sameness they followed unquestioningly. Jonas's mother and father provided family leadership for Jonas and his sister on how to follow society's rules and rituals such as the telling of dreams and precision of language.
2) The assignment of duties happened at the Ceremony of Twelve. At 12, in the community a person is considered to be an adult. They accept the duty chosen for them by the community's concil members. The council has observed them, taken into consideration their interests and their community service work trying to correctly choose their lifetime career path for them.
4) The Justice system was three strikes your out. A person is releasd on the third strike. (This had to be a major offense) Released from society meant that they were killed. This is a very strict justice system. The reason for this justice system was to encourage sameness and keep the totalitarian government in control. If the people started breaking laws, questioning and acting out against the government obviously major problems could result - even the overthrow of the government.