I definitely get obsessive too and need to match the pics! haha the character I'm doing looks different in every picture I have of her
and it's driving the perfectionist in me crazy!
Back to your costume:
From what I can gather, the outfit with the yellow stripe is a different transformation of her; it looks like it's a different outfit than the one you're trying to do, so I wouldn't bother with the stripe.
As for the pleats, maybe iron them and try it on? If the tops of the pleats spread out funny when you move, then stitch them down for a little bit on top. Sometimes it's fine without the stitching.
About the spandex band, do you mean that white "V" shaped line above her skirt? I would say yes, stitch that to the skirt. I would also suggest making it a tube instead of a flat band and putting some batting inside to make it a little thicker... the sailor scout outfits all have that little roll above the skirts that's not just flat.
Last but not least, the change to red sounds good
(PS: I've never made a sailor scout costume, so I hope I don't lead you the wrong way... I'm going by what I've read/seen and what I know from the other costumes I have... but I'm happy to help!)