I haven't thought much about the many questions you all ask. My usual is about typical of D&D assumptions, I think. Magic is present but not ubiquitous like Eberron. Setting will be a frontier Barony on the edge of The Wilds, a place where all races mingle and all sub-races may be found to some extent. This Barony is built on the ruins of an ancient kingdom, and the Baron's castle re-built and expanded the palace of the ancient king and subsumed other nearby structures. (They built things smaller in those days.) These are rumored to include a temple and a wizard's tower. Some parts of the ancient construction have portions that have not been visited in recent memory, and strange noises are occasionally heard emanating from the deepest parts of the basements.
How does that grab everybody? Actually, it came out sounding more 'haunted-housy' than I intend. But there is a dungeon entrance right under the Baron's castle. I don't know the details of Gary Gygax's Greyhawk game, but I have heard some things and that's kinda what I was going for.