Star Wars IV: Was Darth Vader meant to be just a general of the storm troopers?

well he started up writing it as one story but broke it up into six parts and he made the last 3 parts into a movie because in 1977 they didn't have the technology to make the first three and lucas wrote three more star wars movies supposedly that take place after 4-6. But back to your question the only person ranked higher than Darth Vader is the Emperor.