The empty chair is not Krennic's. Krennic's chair is occupied by Tarkin in that scene.
Regarding the
Death Star and hyperspace/having to orbit Yavin... It followed the
Falcon's course. The
Falcon flew straight to Yavin, dropped out of hyperspace, and then flew around the planet. So the
Death Star came out of hyperspace in the same relative place a few hours or more later. If they'd known in advance that the base was on a moon on the far side, they probably would have set a course to pass above or below the gas giant and emerge from hyperspace on the side where the moon was.
Regarding the Biggs-on-Tatooine scene... It never worked with the timeline of the movie. He was visiting home after graduation and before he reported to his first posting. He told Luke he was going to jump ship at their next port-of-call and try to contact the Rebellion. Given Luke makes it to the Rebel base where Biggs already is roughly three days after the day the
Tantive IV is captured, I really don't feel he had enough time to do what he said and have enough rep with the Rebels to be able to vouch for Luke. My headcanon is to split the whole deleted sequence into "Luke sees the space battle and goes to tell his friends, who don't believe him" on the day of, and "Luke wistfully remembers when Biggs came to visit after his graduation" a few weeks (or something) earlier.