Steve,
I think I agree with all the points here. The curvy portion that I had along the 'back' wall, was supposed to be similar to Webber Canyon in Utah, which I-80 parallels. The 'blob' in the center of the room, I had more of Sherman Hill in mind, which I've also been over on I-80, which follows the older routes of the UP in that area.
The way you currently come into your yard, along a curve, it reminds me of Green River, WY, where at one time, traffic was split for different portions of the West Coast. You might want to look at these areas on various satellite images that are available on line. I think 'Trains' magazine also just have a feature on Sherman Hill routes, or did in the last year or two, which you might use as a reference.
I think single track is appropriate if you're going to build a 'climb the hill' type of layout. Has the room got any sort of closet, that might also give you some additional space? I think you'll get something you'll like soon-then its off to the races!
Carl