Dear Uhrwerk and TerraSame,

thank you very much for your replies. They were full of important information for me.

I'm confident that I can now do the next steps.

Maybe one more question:
My port, where the containers are stored, in reality is nearly a plate and the whole plate has the same look (concrete) but with many of different road markings. Do you recommend me to realize the road markings with individual plates and different textures (which has integrated the road markings), or with sprites, ..? Especially the curves I don't know exactly how to do best.
At the borders of my "main-plate" a number of normal streets (asphalt) should be connected. How should I do the corners of grass, between the port-plate and the streets? I tried to use terrain and paint it with different textures in GED, but I failed. Do you eventually know a tutorial which explain painting terrains in GED more detailed than the "Level Design Tutorial" on 3DGS-hompage does?
In common, I would be thankful for hints how to realize a lot of different textures on the ground of levels (grass, roads, road markings, different soil conditions, ...). I hope I could convey my problem to you comprehensible!?

Thanks ones more.