Buildings can be downsized to smaller establishments and track length is dependant on how many cars on a given spur and how long the cars are. Narrow gauge runs far shorter cars than standard... two 18' boxcars will take the place of one standard, and if you make or buy them even shorter{4 wheelers} you can fit more....it just depends on how they're sized.
Also, and this is strickly builder wishes- a lack of buildings can be overcome by added trees and scenery details to make up for that...even a small stream running diagonally across the layout with small bridges over them....your call, but one could easily make for plenty for the eyes to take in.
Just my 2 cents....
