Hi Ted, no plan is boring, especially with two trains.
I did the following; I added 2 O-27 switches, make sure to get the non-derailing versions. This way you can leave it unattended and on the turn the O-27 train will run opposing the FasTrack train (which I think looks cool). It does require 2 custom cut pieces (highlighted in green). But O-27 is the easiest to cut ever.
For the FasTrack I added a passing siding that is long enough for a starter set. So you could have a train waiting on the siding, pointing in the opposite way of the other and have quite a bit of variety. There is an error in SCARM for FasTrack with the O-31 switches, so you must have the 1 3/8 piece always connected to the O-31 switches until it is corrected in SCARM (highlighted in yellow).
I also added your 16 inch square in the middle. Let me know what you think or if you have questions.