Ok, so the LMBG unit is now: Chie, Mai, Chika, Kaoru, Koharu, Arisu, Yume, Wakaba, Yukimi, Reina and Miyuki. And I don't doubt that the ranks will continue to grow. So now the question is: Who's next? It's a little too childish for Risa or Mary to want in (unless the girls do what they did to get Wakaba). Miria and Rika are in a group already (though they could still join up). Perhaps it will be Momoka or Kozue? Or Hikaru to counter Reina?
(The list is from the project-imas wiki, and I think is roughly in order of joining; Miria, Momoka, and Nina were kind of retroactively made founding members in Starlight Stage, presumably so they didn't have to cast several VAs for one story.)
Updated
*grip*Ah, is that so?
Cinderella Girls Theater
劇場第576『一番年上!?』
Theater Episode 576 - The oldest!?That's right... Because till now there wasn't a single job when I was the oldest one...Big Sis Wakaba
(20 years old)Ah... When it comes to the oldest, Miss Wakaba is...Older... I see, does that mean that Miyuki is the oldest here!?*grip intensifies*And in this way, Miyuki also got into L・M・B・G—!
Little Marching Band GirlsO-K! Including Wakaba, Big Sis Miyuki will take care of all of you!I mean, I did tell you Wakaba is technically "an adult"...Even though I'm a middle schooler, I'll be in your care, right~♪Welp, that kinda makes her "an adult"...Miyuki... Let's do our best together~Yup! As everyone's older sister, Miyuki will do her best, right!Just because you're older, don't even try to act bossy, OK? In the end, all of you are just my underlings.