Hello!
I don't have a specific number of chapters in mind, but it would be something like: common route 4 chapters and each heroine route 3 chapters. So something like 16 chapters maybe...
The common route is the route that sets up the relationship between the characters. After that, depending on the choice you made earlier, you either go Angie's path, Melope's path, Saki's path, or Theresa's path (basically, which girl you want to romance).
You are right when you say that Mc and Angelica are the two main core characters, but that doesn't mean you have to romance her if you don't want to. Angelica will be an important character in every paths, but depending on your choice, you will have the option of having the story focus on another girl as well as a new main member. After that, well my job will be to make every path interesting!