The primitive is like graffiti on a wall: We need a surface on which to draw.

Thus we have to create a dummy shape first just so that we can add more complex shapes with FastCarve.

This is not intuitive.
Let the user create new objects without having a base object.

FastCarve should be able to draw a shape in 3D space. We can press x, y or z to flip the plane on which the primitive is being drawn. (This feature is there in SketchUp).

This may look trivial, but if we can draw more complex primitives (e.g. with Bezier curves: see suggestion #12), then this would become extremely powerful tool to create new complex shapes.