At some point (especially in the hanger right before they escaped), sure. But I seriously doubt it [troops missing on purpose as to track them to the rebel base] was happening from the second they landed on the Death Star. That strains credibility by quite a bit.
No, not right away. But as soon as they bust the Princess out, I’d say the plan was made and orders given. The only scuffle before that is when Luke n’ Han are dressed as troops and take em by surprise.
Maybe I’m wrong and they are supposed to be terrible with aim and the whole thing is supposed to be silly, that’s just not how I see it.