Notes:
The modeling phase creates all of the major world components. The creation process includes defining the physical shape, color, texture, and internal animations of those components. It does not include interactions between various components.
It may not be necessary to model all of the components. Many pre-built models can be purchased or used. Spend the effort (time and/or money) where it will have the biggest payoff.
The choice of modeling tools is dependent upon the experience of the modeler. Generally it is better to use lower resolution models for X3D (due to web delivery and potentially limited capability display systems).
The model needs also to be colored, textured, and animated.