1. I haven't been on
DCL yet, and neither has my friend, so I don't know how Mickey has been presented on the ship. I just know my little ones said they wanted pictures of Mickey in his "sailor uniform" as seen in the commercials. I don't have the impression that they think he's running the ship, but maybe on board it's presented differently.
2. In general, yes. About captain specifically, no. I just don't see it. For kicks, I just asked my kids to name a famous captain (outside of earshot of each other). All 3 said, "Captain Marvel." Very unscientific, and probably not valid a few months ago, or a few months from now.
3. I was essentially referring to Piaget's stages of development. Young kids don't get, or think, in terms of symbolism or abstract thought. If they see Mickey/Minnie as the actual captain running the ship, that's one thing. But, if they see them as dressing up for the occasion, then any symbolic meaning to the change will be lost on them. That would just be too abstract for young kids. They would just see Minnie deciding to play dress up now too, without reading anything into it.