Can't wait to drive on this track from my hometown. where are you from? let me know if I can help you with something, possibly with the supply of current pictures of the track and buildings.
Drawing splines for outlines (long and boring process....) move spline vertices to surface with a script, extrude to meshes, select top surfaces and move along z-axis for different heights (long and boring process....) select all top surfaces and assign google maps texture select all other faces and and assign a generic house face texture (50% random) Here is a script which may be useful for big skyscraper cities: Sadly not very helpful for building a small town in Germany.
You're straight up killing it man. This looks like it could be a top tier mod track. I even will get it if it is a paymod. Please finish it. I love the Sachsenring too much.