Short answers, pulled from the story.
The 100-page contract for The Empire Strikes Back was signed on the 21st of September 1977. This agreement dictated that 20th Century-Fox would distribute the film without creative input while receiving 50% of gross profits up to $20 million.
Leigh Brackett completed her first draft titled Star Wars sequel from the adventures of Luke Skywalker in February 1978. She died of cancer on March 18 before Lucas could finalize the script with her, forcing him to write subsequent drafts himself.
Principal photography began on the 5th of March 1979 at the Hardangerjøkulen glacier near Finse Norway representing the planet Hoth. Filming occurred during a severe snowstorm with temperatures between minus 30 and minus 40 degrees Fahrenheit.
Industrial Light & Magic developed approximately 600 special effects shots for The Empire Strikes Back compared to 360 for the original Star Wars. Up to 100 people worked daily on these effects including Richard Edlund Brian Johnson and Steve Gawley.
The film's world premiere took place on May 20 at the Odeon Leicester Square cinema in London dubbed Empire Day. North American audiences saw the film open mid-week on May 21 leading into an extended Memorial Day holiday weekend.