I think the Luke/Leia thing very obviously was foreshadowing, or at least a hint. Maybe they hadn’t decided definitively that was the road they were going down yet, but this more than conveniently left a strong opening for it. No one will convince me it wasn’t at least thought of at the time. The fact that she alone senses Luke in a very similar way to Vader in the same scene is too much to be a coincidence.
As for the Lando and Han line, pretty sure it’s only to emphasize how similar the characters are in terms of personality and background.
I think you’re right. Your answer makes the most sense. I think it’s because Han and Lando are so much alike. I thought maybe that scene was trying to tell us something initially but it’s hard to know what.
I will say that since it was sort of Lando’s fault that Han was frozen in carbonite…obviously it was still Darth Vader who did it…but since it was sort of Lando’s fault, Leia and Luke were awfully forgiving toward him. But I guess Lando did help them escape after all.