Sean,
What is XTRCK?
I would think about using the foot bridge over the track as your main entry point at the bottom of the photo. Then you could use the PVC pipe (12 inch inside diameter?) to construct a tunnel at some other point. That way you won’t have to worry about people walking on your tunnel and disturbing the trackwork underneath. (Ask me how I know about this. 
)
You said that you don’t mind moving dirt, so how about using the rest of the track to create an elevated line that wanders back and forth over your mainline? It appears that the mainline is already on a slope, so the upper level could be accessed by a pair of switches at the highest point of the layout. The upper line then looks like it might be able to be level, and by the time it gets down to the bottom of the photo, there should be sufficient elevation to cross over the track. If you put a gentle 2% slope to the upper line, you can cross over sooner. You can use a tunnel one time where the lower line uses the tunnel to cross under the upper line, and a trestle or other bridge for the upper line to cross back.
This will give you trains appearing and disappearing, making the layout appear bigger.
If you are not married to straights in your oval, you might give some thought to some gentle s-turns to make the track work more interesting. Scale sized trees and other folage will aid in this, as well.
As time and money allow, add in some sidings for industries for operations. Just watching your trains chase their cabooses will get old, after a short while.
In any case, you have a great start, you have track on the ground. Good job! Keep up the good work.
SteveF
