Nice idea. It reminds me a bit of 20,000 Light Years Into Space.
Hadn't seen that one before, there may be some similarities indeed, though if I manage to complete the game as it is my head right now, it should play quite differently.

What kind of "point of view" does this game use??
3D/Isometric like age of empires III or a free camera etc... :?
I'm leaning towards something Warcraft-like, with "zoom" getting you between overview mode and near-3rd-person in fixed steps. There are a few problems with that approach given the world scale.

Are you going to include forest and foliage or just pure rocks and cliffs??
Yeah, I want trees, but being mostly cosmetic, they're going to be somewhat down the priority list... so it'll pretty much depend on a lot of factors, from models and texture availability to development time remaining. 3 years ago there was a GLScene "Forest" demo with thousandths of trees, today's hardware could probably handle tens of thousandths...