Diego said:

Speaking of which, what the hell was Luke's plan for rescuing Han? As much as I love ROTJ, I've never been able to make any sense of the plan.

Here is how I see it. First he sent Lando to infiltrate and get familiar with Jabba's habits. He found out that Jabba care about his rancor and that his worst punishment is throwing people into Sarlacc pit. So Killing his rancor would ensure "Sarlacc". Luke knew he couldn't defeat all the thugs and bounty hunters packed together in Jabba's palace so he intended to confine them to the sail barge through "Sarlacc punishment". In order to guarantee Solo will be part of the punishment, Luke sent Leia and Cheewie to melt him out of the carbon. He knew he would be stripped of his lightsabre after killing rancor therefore he hid it into R2 so he was able to use it at the Sarlacc pit.

Yes I know this plan could be ruined by a single flaw but still... that is the only reasonable way I can think of.