I made a few additions to the plan, marking out the different levels more clearly and noting where I plan to have the feeder lines connect to the track, and I printed out a 1:1 scale plan. I've left out the center section for now, since I plan on laying down the flat track first before moving on to the upper level. Of course, any large flat space with things going on is a magnet for cats.
I have identified one possible trouble spot on the layout: on the upper left, where the track heading up to the upper level comes very close to the level track. Originally there was this snaking S curve in the plan, I believe intended to add distance for the 4% grade. I kept this, thinking that I could add a rock outcropping or other feature to justify the bend in the track. However, right now two tracks come within 1 1/3 inches of each other, which is a little tight for a curve (Armstrong 1998, 81), but more importantly the rising track is 0.81 inches off of the base at the point they are closest. This means that the track and whatever is supporting it will be intruding into the clearance space for any trains on the lower track. I will need to make a mock-up and see if anything needs to be changed.