@yurirei It's unclear why exactly Maho and Anchovy were made into a pairing, but there are a couple of ideas 1) Maho goes to KMM, a German-themed school, and Anchovy goes to an Italian-themed one. Since Germany and Italy were allies in WW2, that is one reason they could be paired together. 2) Their personalities may have been a good match to Japanese viewers, who saw Maho as the stoic, but competent type, while Anchovy was very expressive of her feelings, but not as confident in her abilities. A good balance for a pairing. 3) There is a scene in Der Film right after Miho and Maho defeated Arisu where you can see Maho stare at Anchovy for a second. It was small, but I have a wild guess that Japanese viewers (who are very attentive of this stuff) saw that and started pairing them together because of that. Though, this 3rd reason is a wild guess and has the least amount of support for it.
As for the "university/college" setting, many of the girls are soon expected to be in university/college so a lot of doujinshi/manga portray the third-years and so on in college settings. It's a nice way of doing a slice-of-life story without having to draw tanks or making a complicated setting. I enjoy it a lot because it allows the girls to wear something outside of their usual uniforms as well.
I hope that helped answer your questions in some way.