other than at the end, Thanos only uses the soul stone once. Against Dr. Strange.
They definitely said this was Thanos' story arc.. if Thor had won, it would have been his hero's journey.
Russo's confirmed, after the snap, he's in the soul stone (or a soul world).
They flirted with the idea of having Captain America show up right when he saves Vision at the very end... because his main arc will be the next movie. So, Captain takes a bigger role in the next one.