Sorry if I'm missing something, but why would Luke go to Dagaobah first? Rescuing Han should be his first priority. In fact, Irvin Kershner felt strongly that Luke should go with Lando and Chewie at the end of Empire, and settled for the line about "meeting at the rendezvous". Plus, Luke doesn't know that Yoda's going to tell him "no more training etc.", he thinks he's going for more training. They wouldn't rescue Han without him, and they can't wait for Luke to finish training. Every day is a day that Jabba might get bored and kill Han.