Also what were the roles of the government leaders outside of the party? It seems so different from other countries/eras.
The General Secretaries of the Communist Party WERE the heads of state. The Premier was the head of the government, while the General Secretary was the head of state. So, Brezhnev, Andropov Chernenko, and Gorbachev were GenSecs, not Premiers, while Lenin, Stalin, and Khrushchev were both. When Khrushchev was ousted, the Central Committee forbade both posts to be held by the same individual.