Two more tips--put a least a small layer of foam to build on. Most landscape goes both up and down from the track. Give yourself the option of going down. It will also make the placement of trees and figures easier. Plywood is really hard to mount stuff to.
Paint the foam immediately with cheap brown latex paint--usually the paint store will have a batch that was mixed the wrong color that they will sell at a price to just cover materials. Then paint blotches of a different color brown to give it a mottled camo-effect. Then when you add scenery, you won't have a solid color showing through. The brown, at least will not look like the plywood or foam and will be a big psychological lift.