Quite an ambitious project indeed
What kind of size are you thinking of for the boards? Are they going to be more diorama-scale (like those 'army-on-parade'-ones that pop up every once in a while), or big enough to actually play games on?
I personally would love to see a giant alpine mountain range/forest (and not just because I would shamelessly steal some of those ideas), but I think Venice
40k would look better on a smaller scale