Thanks for your kindness, Mark and Mike, and thanks also for the opportunity to share some of what I've learned through OGR. Fortunately, Mike's layout can be carved up fairly simply or I would probably be over my head. Mike's selection of long pieces also helps to keep from getting stupidly small blocks.
The lower level track on the right side can be similarly divided back to the beginning of the yard. Sectional track in curves usually need a drop right in the middle so the curve on the lower left is pretty much defined.
I'm guessing that will be an engine shed at the end of the wye on the lower left, and will those tracks also be switched on and off? Looks like that branch can be isolated at the turnout leading to the wye.
That will get things narrowed down to the yard. I'll get something marked up later this afternoon.