Thanks guys. This is going to be a diorama. I'm building it for a LUG display at the Rockefeller Center Lego store, so it's limited to the size of the display cases. However, once it's been displayed for awhile, I would consider expanding it.
Here's an update. It doesn't look that different, but only because much of the progress is structural. The platform can support its own weight, and it's attached to the base.
This shows some of the framework holding the base together:
In the previous shot it was just tacked together and prone to falling apart.