The good thing is that we can roughly see from the intro (backed up by the achievements) where the story will go. The girls are grouped and the traits and such say they will affect one another so I don't think any of them will be isolated.
To be fair, it's not quite clear yet whether the current grouping is actual groups or simply that they're the ones in the game right now. For example: Selina, Paris, Chloe, and Jordan are grouped together despite Selina and Paris currently having no best friends, them seemingly not interacting with Chloe and Jordan, and that they're a mixture of first, second, and third years. But then again, maybe the will become a group later on? Hoo boy that'd be an interesting group chemistry that I'd love to be in the middle of just to experience the potential nuclear explosion.
We also have to consider that dev has 11 planned endings which include solo/group/harem ending. So there definitely be solo routes for some of the girls. Then we don't know either how the game will handle if the player only show interest in one/some of the grouped girls and not all of them. For example: what would happen if you have high love with Ella but low with Lydia and/or Chelsea? Do we just still get content with Ella or do we get no content at all from them because the others don't like us?
You're right though, I think the dev made it quite clear that the game will pay attention to group activities with how many of the achievements seem to involve multiple girls. I really hope the solo routes are only for at most 3 girls and not too many of them.