Well, maybe I'm disqualified because I actually (barely!) started this map before the announcement, as part of a collaborative project in my local writers group. But I'ma thread it as a WIP anyway.
1 & 2 - This is pretty much where I was when the challenge was announced: our chosen site in England on the River Ouse, and Buckingham palace set in for scale for the baron's castle on the hill.
3 - Added a terrain heightmap with a gradient ramp*. The idea is, the baron's castle sits on a hill overlooking the town. There is a sheer cliff dropping from the castle's prominence down to the river. There will be bridges upstream and downstream from the cliff.
4 - The first gradient ramp sucked so I redid it. Much happier with this approach. Added a little elevation scale to the side, also. Is 65ft a good height for a modest cliff face?
5 - The grayscale heightmap.
* I learned about the Gradient Ramp feature thanks to Cartographer's Guild! Been using Photoshop literally since 1990, and I keep discovering new features! I also learned about the Shape Burst here. Keep the tips coming, CG! Yu guyz rawk.