Browser-Based Game Terrain Graphic Design

I am designing and programming an online multiplayer roleplaying game (MMORPG) that is completely web browser based and works in all modern browsers. I need some help making some of the terrains a reality, and have good textual descriptions of what I am looking for, but need the skills of a graphic artist familiar with computer game terrains or the like to make these a reality. I have a couple of template drawings that I can give to the winner to build upon and get a better feel for what I'm looking for. The basic areas are: 1. town area with a keep in it 2. inside the keep 3. wilderness (Includes lake, mill, caves, forest, field, graveyard) 4. sewer (both keep, wilderness and town connect to this) 5. caves (One or more similar ones) The basic size I am looking for now for each region listed above is around 5000x7000 pixels JPEG, and the detail is high (Total file size around 15 megs). The look and feel is important, and is medieval, but with a real-life tint. In other words, it should clearly be a computer game world, but look somewhat realistic. A good example is what age of empires terrain looks like. The texturing, shading and viewpoint should make everything look slightly 3D, even though the game itself is actually 2D and there are no true 3D graphics.