To my best ability i will answer you questions.
1) that screenshot you showed before is perfect make it like that.
2) The races in the surface world are trolls, murlocks, spiders, wolves, satyr, kobold, and only a few humans. All the big races are in the sky. The races in this map should be like wild animals.
3) Make the map as large at possible.
4) Yes make caves, and hard to reach areas and secret areas.
5) For now make it a gold gathering game, maybe even make some gold places hidden.
Players will also have their airships.
Hope that helps.