I am working, slowly, on a project. I spend most of the time working on ideas because I have a problem.

I'm trying to create a RTS game with and there are some major problems that I am foreseeing. The first is the issue of a graphics engine. I'm looking for something that is able to easily handle (or make it easier) to use 3D spherical maps. The problem of producing the spherical maps is another problem. With the scale the game it will have I don't want to bother with complex unit models or shading for anything but the biggest things, unless I somehow find support (fat chance). Textures are minimal, physics minimal, and most of the graphical enhancement will be secondary to making a playable game.
So, to ask a direct question, should I make a shell engine to visualize the game or find [a free] one. If I should find one, what would be good engine choices. I can write in C++ and can use Win32, I also have a minor knowledge of DirectX. Lastly, I need some help generating the maps on the spheres.

Any help?