Did the peoples of any worlds know of Thanos' plans?
They knew of Thanos. He had a reputation for his wiping out half of the population (since he left half of the witnesses alive, like Drax). It's likely that what people did not know was that he wanted to use the infinity stones to wipe out half of all life in the universe. Gamora knows of his plan since she "worked" for him, and he sent her to find the Soul Stone. Other than a few exceptions, I don't think it was well known what his exact plan was.
In short, people knew who he was and that he killed half of the planets that he conquered, but they probably did not know that he was trying to acquire the infinity stones to do this on a universal scale.