That was super cute. Muse and HTT together! That's awesome.
Dunno why Mio didn't go up against Nozomi for the bust size competition. Mugi has got a huge bust too, but everyone knows Mio's is just a little bit bigger. Dunno if it would have stacked up against Nozomi's, but still. I've put a lot of thought and time into thinking about their breast sizes, so I know what I'm talking about.
Answering super-late, but the girls from pages 2 and 3 are the girls' dorm-mates their freshman year in college; they're also a band, "Gang of Girls". (The manga continued for a school year past the anime's ending, paralleling Yui, Ritsu, Mio, and Mugi at college with Azusa, Ui, and Jun in high school together with new characters Nao and Mugi's little sister figure Sumire.)