ITT: Headcanon discussion
1. This has been addressed pretty well. Why would the Imperials go after a couple of random droids when Leia was right there acting as a decoy to get their attention? Since she didn't actually have the plans on board anymore by the time they captured her, she had all kinds of plausible deniability on her side; sending the droids off on their own to reach Kenobi was her best bet to ensure that the Death Star plans got where they needed to go. She had planned this--that's why Artoo's message for Obi-Wan included Leia apologizing for not being there personally.
2. You're going to fault them for having a plan B? Plan A would obviously be 'keeping them all prisoner and not allowing an escape attempt in the first place', of course. The trash compactor thing wasn't part of anyone's plan--not the Empire, and not the Rebels. It was fog of war, Murphy's Law, what have you. The Death Star was so huge, they couldn't keep track of everything that was happening during Leia's rescue and escape--this is made clear by the fact that they didn't know our heroes were in the trash compactor, and therefore didn't shut down the trash compactors and just take pot-shots at them from the hole in the ceiling...and the fact that the Falcon and all its passengers were able to escape in the first place.
3. There are figures that place the DSII at 160 km in diameter, and others that place it at 900 km. If it was closer to 900 km, that puts it on par with Saturn's 'large moons', and if it's appreciably bigger than the original, then that would easily put the original in the realm of Saturn's small moons. Y'know, a large small moon. (Incidentally, if the DSII is 900 km in diameter, and is twice the size of the original DS, that would make the original Death Star the size of Mimas. That makes me smile. Let's all say that the Death Star is the size of Mimas.)
4. That should have happened, yes. Still, the official fuzzy-wuzzy feel-good canon explanation is 'all that energy from the DSII exploding created a wormhole which most of the debris fell into, therefore No Endor Holocaust. Yay!'