Hi,
For tracking scale you need two markers. In AE's tracker controls you can select a combination of scale, position and rotation tracking. This should be fairly easy as long as your two markers are never obscured by the models.
This is assuming that you are not digitally adding in the floor, because then you'll need a more complicated approach since you'll have parallax. You 'd need 3D tracking.
Barend
Raamw3rk - digital storytelling and visual effects