This would be the first thing I would try. Since the geometry of a hexagon is not that complicated, you might want to consider to generate it procedurally. Alternatively, you can create the model in a tool like Blender, export it as glTF and then load it via GLTFLoader (read the following guide for more information about this particular workflow three.js docs).
Raycasting in general does not account the opacity of the object’s surface. It just works on geometry level. Besides, read the following topic to understand how to orient the hexagon mesh always towards the camera: