Dyson sphere? It sounds familiar but remind me what it is. would it be able to support the flat, warm in the middle, frozen at the edges idea? (or actually, a planet could support that to, as long as it always showed the same face toward the sun.)
I think the setting should be "firmly" fantasy, having a sci-fi explanation for that it's built on would be fine. It could be hinted at for the GM, but never fully revealed.
Anyway, I think this bit is the most important to get down before starting the work. The basis of the universe kindoff serves as the foundation for the setting, and makes it much easier to add to it.
I can add a subwiki to this thread, but I'm not sure if where ready for that yet.
SGL.