Toritsu Mizushou first appeared as a light novel by Hikaru Morozumi. The manga series doesn’t seem to share very much with the novel other than the setting, so in a way you might call it an authorized doujin.
Shinobu Inokuma’s series before this was Salad Days, and you can find similar character designs there. One character in Salad Days is cloned into an entire baseball team in Mizushou. But unlike Salad Days, Mizushou is much more focused on major characters, and story arcs tend to become longer as the series goes on.
All in all, great comedy and good soap opera. Explicit sexual content has been surprisingly rare, more or less equivalent to Kenichi Sonada’s Gunsmith Cats or Cannon God Exaxxion.
Inokuma has a web site, “The Garden Plot“ at http://saladplanning.pro.tok2.com/main.html