Another work by Takeshima Eku so at the very least we know there are going to be a few heartthrob moments. Looks pretty fun so far! Also thanks for the translations!
Basically:
https://jisho.org/search/appare + "dan" (basically "group" or "squad", or a suffix indicating a group name).
So it's indeed in reference to their group and is something like "The Superb Squad", or something similarly substance-less.
(Edit: I believe the way it's used in the English bit on the raw cover—"APPARE! Girls in Okayama"—is more like, "Bravo!", a possibly-slightly-antiquated thing you might say during, or in place of, applause or ovation and the like. Make of that what you will; it would seem to amount to roughly the same thing either way.)
As short as this is it is overflowing with sweetness. I could have read this for many many more chapters since it was a very enjoyable read, exactly as expected coming from Takeshima Eku.