This looks like a spectacular layout in the planning! I am an S scale operator and have a medium sized custom layout with 18 months of operating experience with it. I offer the following thoughts on the plans. My minimum radius curve is 30" which scales to O-80 in O gauge, about the same as yours. We adjusted the track plan to include easements. If longer cars and engines are in your fleet the easements minimize the lurching as they enter the curves. We also deleted all the #4 turnouts in favor of #5 minimum, even in the freight yard ladder. I feel the trains look better and seem to operate better.
It looks like there are no reverse loops in the track plan. My original plan had none and I thought I did not need any but the plan was modified to include some. I am surprised how frequently I use them now that I am operating the layout.
My S scale turntable is 22", the same as 30" in O scale. As people recommended above, this is a good size, but it will still be a little short for the largest articulated steam engines. Be careful starting a curve on the approach to the turntable, a short length of straight track is desirable.
I can only wish I had as much space as you have. I hope you enjoy the layout for a long, long time.
