That all sounds good, Mark. I had forgotten what track you already have and was too lazy to look back through the thread. 
Like you said, those details aren't so important because adjustments will have to be made as you build. I did want to show you the difference though.
There are other S curves in the passing siding. Those can be minimized by substituting Ross #11 switches, but I didn't like how it looked, so I didn't include a photo.
I don't like legs, so that has always been my problem with the Mianne bench work. I have little doubt you can support the layout with the brackets you described. Good luck with the test.
I added the additional extension to the passing track mostly because I misread your earlier comment. However, after I added it, my thought now is to be able to pull all the way in on one extension, then back all the way into the other extension and be ready to pull out without clogging the main. Without the 2nd extension, you have to back far enough past the switch blocking the main so you can pull out. Just food for thought.
Train pulled in:
Train getting ready to pull out w/o using upper extension blocking main:
Train getting ready to pull out using upper extension w/o blocking main:
