Short answers, pulled from the story.
Orson Welles signed a contract with RKO Pictures on the 21st of August 1939. The agreement granted him unprecedented creative control to act in, direct, produce and write two films.
RKO Pictures awarded Herman J. Mankiewicz credit alongside Orson Welles in January 1941. Robert L. Carringer concluded from script records that Welles's contribution was definitive after condensing and rearranging drafts.
The meaning of Rosebud remains unexplained by any character until the final scene where only the audience discovers it. It refers to the sled owned by young Charles Foster Kane before he lost his fortune.
RKO hired Gregg Toland on loan from Samuel Goldwyn Productions in the first week of June 1940. He utilized deep focus photography and low-angle shots to break studio conventions during filming.
Citizen Kane returned to public attention when praised by French critics such as André Bazin and was re-released in 1956. The film later stood at number one in British Film Institute Sight and Sound decennial polls spanning 1962 through 2002.