looking at the 2" foam...thinking about making it 4" thick and gluing it staggered, having enough depth for a decent ravine, and put the city section with streetcar in the upper right corner....
my daughter is planning on moving out in August (hopefully), so I am going to start with this section being the same length as the longest wall...I am also thinking about building the city area above a small , thin staging area. I am looking at cheating a bit and making a simple loop with Tomix Wide Tram track that uses 103MM curves....the only issue is finding a 6.5mm sheet that will work for the rest of the street...
Various sheet building materials may be nominally 1/4" thick, but are often less. It may or may not be close enough for your purposes (or be shimmed with other materials).