You do not use Civil3D? If you try to program all those things you might better buy a Civil3D and use that.
At the moment I work on an application that does surface creation, volume calculating, sections of surfaces, profiles from 3D polylines, and so on. It is quite a lot of work, especially the math to calcultate intersecting triangles and the height difference. The application is meant for BricsCAD users and AutoCAD users that don't need a full Civil3D.
You can't create all these things in a few hours, you need weeks or months of develop time. There are also cheap or free earthwork programs you can use. Maybe that is an option?