Hi Olve,
I'm not sure that I can answer all of your questions but I'll do my best.
I use the FS2004 Terrain SDK to make photoscenery and it works just fine. Before you can compile it, you have to cut the edges of your image so they line up exactly with the LOD13 rectangles that you want your photoscenery to cover, and you must know the northwest and southeast corner coordinates. Once you do that and complete the .inf file, you can compile it and it will chop your image into individual LOD13 areas automatically. The best way to completely understand this process is just to read the SDK and try it out yourself. As for the coast, once your photoscenery is placed it will cover up any default coast, water, or anything else except specially placed 3D objects. In order to get the reflective water to show in your photoscenery you must create an alpha transparency where the water should be. To do this, I use Martin Wright's ConDXT available at http://fly.to/mwgfx/. If you want to make a G2k4 scenery in the same area as your photoscenery, I believe the photoscenery will be on top of whatever you create in Ground 2k4. Mesh can be included along with these other types of scenery in the same folder. However, if you are implying that you want to manually edit the mesh (with the Ground 2k4 re-mesh function or something similar) be warned that this is definitely not the best process to use, especially for large areas. The way most people create mesh is by downloading digital terrain data from the internet. This data is usually collected via satellite in a grid pattern, with an elevation reading taken for a set area, such as 10 square meters, 30 square meters, or 90 square meters. Data taken at smaller intervals is, of course, more accurate. You just have to compile this data with the terrain SDK in much the same way that you make photoscenery to get a mesh scenery. Once you place an object with Gmax, all autogen objects immedietly around the Gmax object become excluded. If you want to get rid of an airport building, custom object, or an area of autogen, you need to make an exclude file and in it define what you want to remove. This process is described in the BGL Comp SDK. And lastly, you should be able to put everything into one folder as long as you don't have new landclass files; those need to go in a seperate folder.
Hope this helps!
-Scott

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