Mark,
Just so you know, a turntable is still an option, it just limits your landscaping options unless you follow through with your idea for a removable platform in that area. And as you can see, I was able to add some whisker tracks. They vary from ~12" to ~30", but that depends on where you specifically place the turntable.
NOTE: Sorry about the 3D image, the turntable automatically fills the space below.
One caveat is that I don't know how deep the turntable pit is, so I'm not sure about clearance for the staging yard. Also, the version with the passing siding presents some grade challenges if you want both the turntable and yard. It should be noted that the turntable and whisker tracks, when rotated, could also fit where the lower loop is. As you know, the idea for the staging track started with just a single track so you could be staging a new train while the other was running and it blossomed into a yard. 
One final thought that I haven't modeled is that if you take out the yard, the blue track could wind beneath the upper level to make the run longer. However, access would be limited, but I wanted to throw the idea out there because I don't think you have enough to think about. 
