You can pretty much create as many terrains as you'd like. Since this game is going to be somewhat abstract anyway (e.g. distances are not to scale) you could use gradations of "deep space" to make some systems farther apart or even inaccessible without certain techs, just by creating more than one kind of "ocean" with different movement costs, required techs, etc.
There is an obscure XML file that I believe controls the Y-height of terrain. When I looked at it it seemed like a bunch of numbers, but someone with some time to do research could probably reverse-engineer it to make terrains actually 3D (not that it'd be that helpful, as you wouldn't build on the underside of a planet, so maybe a semi-sphere is enough).
IIRC each tile is actually composed of 4 corners of the texture file, so blending will be a real toughie until you've figured out exactly how each texture file is fit together by the graphics engine (which is beyond the reach of even the SDK)
There is an obscure XML file that I believe controls the Y-height of terrain. When I looked at it it seemed like a bunch of numbers, but someone with some time to do research could probably reverse-engineer it to make terrains actually 3D (not that it'd be that helpful, as you wouldn't build on the underside of a planet, so maybe a semi-sphere is enough).
IIRC each tile is actually composed of 4 corners of the texture file, so blending will be a real toughie until you've figured out exactly how each texture file is fit together by the graphics engine (which is beyond the reach of even the SDK)