As for the collar, I'd go with something shiny, like satin. For the fuku, white spandex is used by most cosplayers. I guess I'd go with tulle or something for the sleeves, I don't now what else could be sheer...
Yes, the skirts are gathered. It wouldn't really work out with pleated skirts anyway.
~Work in Progress~
Yayoi Ulshade/ KyoryuViolet (Zyuden Sentai Kyoryuger)
Nazo no Shoujo (Kamen Rider Gaim)
Kagura/Toq 5gou (Ressha Sentai Toqger)
Akiko Narumi ~Wedding Dress~ (Kamen Rider W)
Yellow Power Ranger/ Trini Kwan ~Super Megaforce/Gokaiger Version~(Mighty Morphin Power Rangers)