Not off topic at all! The .0 does refer to later parts of the series. Each one introduces four cast members (as there are 13 in total including Suki). Technically, two of 2.0’s cast members have been either introduced or mentioned in 1.0 The Royal Rebels. Essentially, come the next part, anything that happened after the introduction of the previous part is not considered to happen and you have a clean slate for Suki’s love life at Yanagi high. But you can only date the new four options and not any of the previous ones.
You can actually find all of the bios for the later girls (and boy) here!: https://theartofcsr.tumblr.com/post/164123169173/started-making-character-bios-for-the-illness
Yoko, Sakiko, Kazashi, And Katsumi are The Royal Rebels and introduces in 1.0. While Yan, Rini, Midori, and Kimi are The Bloody Bows and introduced in 2.0. Finally Takara, Natsuko, Haru, And Emiko are The Destructive Divas and introduced in 3.0. So the names are like the group’s name as a whole, but can also be seen as the name for each segment.