I forgot - one trick for the navigation is simple.

Set up the entire scene as normal. When you are finished, create a grouping object. Then parent everything to the grouping. Then scale the grouping object up.
I think you can even parent lights and cameras if I remember correctly.

If the cameras and lights scale too, that would be workable. It would be great if the renderer could do a "virtual rescaling" when needed to get around issues like this.

Download my free stuff here: http://www.renderosity.com/homepage.php?page=2&userid=323368