9/10 ideas:
1. Maybe more than one type of school in game to select, as same as select room in normal.
2. Similar to the first point above. In normal, this is an ordinary school. But may be add some schools with some key subject themes, suck as music school / sport school / cooking school etc. In real, in addition to their subject subjects, general school content is also covered. And those additional school, the school design / uniform design / on-campus staff etc, should also different with normal.
3. Similar to the second point above. Different school may also have different special rooms, such as dedicated rooms like opera room / extra large lecture / lido(I like it very much) etc. At the same time, you can also consider referring to the school theme in other anime.
At last, a strong suggestion, hopefully this game can be selling in Steam platform. Steam is allow the game with adult content, also selling the game in Steam can be more easier to promote.