Also, I think on the SSE thing - considering you get to replay so much with all the collecting of stickers and trophy podiums and whatnot maybe you can do stages on different difficulties with your char on choice - just stages ripped out of the story, for challenge and sticker collecting.
Also, "beating SSE with Samus" could be vague - maybe you have to beat a certain segment with Samus, as in the story forces you to unlock Ridley as you progress. By clubbing his *** with Samus. After all, this is the most probable way for chars to be unlocked in SSE, right?