Gotta agree with JT, that does sound like a great project. It actually sounds like you might be thinking of doing the layouts in an Isometric view.....one of the harder views to pull off imho, but if you think you can by all means I would love to see what you come up with.

About the first picture, I am not sure what sort of scale you plan on having for this map,but that looks like a MASSIVE bridge. I think it would be better if the road from the Mountain Gate eased west of the lake and then crossed at the falls then made its way to the Mountain Pass. This way there would only be the two smaller bridges, each of which have the potential of being defensible from the 2 complexes.

I do like that third map idea of combining them all into one show piece.

I am really looking forward to seeing this develop.