RPLST8, I think it is a very imaginative and well thought out plan. You are certainly using the philosophy when you want more track/layout in a relatively small room, build up. It almost makes my head spin in the complexity, but I know that when you are the one designing it, you grow along with the plan.
I'm with Donald when it comes to access. You look to be a relatively young man who will have no trouble going under, popping up, and lifting the pop up covers (turntable and associated trackage). I'm only a year younger than Donald, so all of that is out of the question for my layout build. I'm also like him, I can't crawl up on anything anymore. I had to crawl under, on top of, and squeeze through small spaces during my working years, and now I wouldn't even think of any of that.
As to track. I am using GarGraves and Ross switches, and I think you can get all the sizes you mentioned that ScaleTrak has available. I did not go with Atlas, because when I was planning and buying, there was a shortage of their track and I didn't want to take the chance that construction could be stalled because of availability. From what I read, Atlas has resolved their issues. I certainly like the look of their track, though I came from an HO background, so I had to get used to O gauge track offerings.
Do you have a friend, relative, kids, spouse who will be helping with the build? An extra hand certainly would be useful. I go it alone, since my wife is in worse shape than me.
I'm looking forward to seeing this layout come to life as you continue on building!!