I just bought the Bachman Thunder Valley. I know I will not use the track that came with it. Mainly bought it for the engine and cars. I'm searching and searching for a book or magazine that has complete plan for a good N scale layout.
When I was in it 30 years ago I did a plan from a book that showed how to cut the wood and how to do the elevation. It showed everything from start to finish with the exception of scenery. Back then it was all plaster for scenery, cork for road bed, and all track/roadbed was laid directly to the wood.
I am seeing that foam is used for scenery, roadbed (think I will still use cork), and also laid on top of the wood.