A 12" wide wheel is going to make for a pretty thick fixture. Are you going to leave the wheel intact? Or are you willing to just use the face (or cut the wheel)? Then you would have an easier time of mounting the wheel face over the hub of the fan.
Aesthetics of the fan, itself, is personal. But right now I dig the look of (no joke) Big A ss Fans.
www.bigassfans.com
Sounds like a cool project!