Well, the recommended dimensions are in the FT itself - just go to model tab and select a different one (3 point clip or 3 point cap is needed for 6DOF). You'll see the default distances between LEDs on the right side of the window - it would be best to use something close to these dimensions. But don't worry if your model's scale is a bit off - you can always change dimensions in the software after building your rig.
As for how this setup might look - your imagination is the only limit
But be sure to check the model gallery tread (both in English and French sections) for some examples:
http://forum.free-track.net/index.php?showtopic=466
http://forum.free-track.net/index.php?showtopic=2