GPU Gems 3 - Chap 29 - Rigid Body Sim

I intend to use this thread for questions regarding rigid body simulations and how to implement such a system. I am following the tutorial that can be found here:

A 3x3 inertia tensor is used in the instructions, but the rotation matrix you get from a quaternion is 4x4. You can’t multiply a 4x4 matrix with a 3x3 matrix. Do you solve this by transforming the inertia matrix to a 4x4 matrix?

The relative position for each particle is used in calculations. Do you have to update what the relative position is in each iteration or do you only do this once?