Terrain add-on compatibility

I'm looking to push the FS9 scenery as far as it can go in terms of terrain mesh and texture and sky textures.

After reading this: http://www.avsim.com/pages/0106/3scene/3scene.htm I can see that I don't have a program to improve the mesh (the 3d element?) of the terrain as i only have the following:

Flight Environment
Ground Environment Pro
Ultimate Terrain

My questions:

1. So, given the above, what program would best compliment these? FS Genesis or FS Global 2008 or something else

2. Would they all run happily together or am I duplicating things here? For example, i'm thinking that if I installed, say, FS Genesis, over which went Ultimate terrain then there wouldn't be a need for ground environment pro - or would there?

3. What would be your order of installation and scnerey priority within fs9?

4. What are your add-on recommendations for the best FS9 Scenery experience?

Thanks guys.