Ghosts are just entities, they're not related to the materials of the real world. They could be only if they're Poltergeists but I don't think that phenomenon would happen in a room like that.
And I'm pretty sure that the phrase "Use what you can't see" is a reference to the elements since we can see them and can't at the same time. But the need to focus the middle image could be a possibility.
Also, I don't think we need to count all the elements. Fire could be only related to the Spirit of 1029 logo, like Gunnr said.
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