Not trying to discourage you, but a reliable geometric kernel takes around a decade of work to develop, for a team of PhDs.

Based on the docs, you've only implemented some very basic topological operations (and rendering, for some reason). The hard part is going to be implementing the rest: boolean operations, offset surfaces, lofted surfaces, blended surfaces, etc. and then there's the problem of version control / edit history. Efficiently and accurately implementing each of these can be a year-long research project in itself... You need a solid understanding of 3D topology, numerical methods, 3D differential geometry, etc.

Nevertheless, I wish you luck! I will check back in a year or so.