All the content on the DLS will do for N-Scale. When you select a scale at the commencement of a project, all this does is to adjust the readings on the built-in rulers; the assests do not change size if that's what you are thinking. In any event, there are more accurate rulers to be had from the DLS.
You cannot have a 4' by 2' board. The boards must be 720m by 720m and your layout will have to sit in the middle of it. The best option is to create layouts in 1:1 scale and convert you N-Gauge plan to full size.
In the real world, I model in N-Gauge and use Trainz to prove my designs. A large N-Gauge layout from the real world will occupy about one-third of a single baseboard in Trainz. And guess what? The same layout in OO or O-Gauge takes up exactly the same amount of space.