Mark: You need to practice bending some Gargraves. :-) It does take some practice, but it goes really easily for me. I litterally hold a strip of flex against my chest and gently begin bending in around my torso...just a little at a time. It doesn't take too long.
Sectional pieces work...I've used several along the Glacier Line. I just like the flex because it's more "railroadee" for the lack of a better word. I really like you can make the curve go anywhere you want...anywhere....a little tighter here, a little looser there...as is in real life.
As far as concerns, just make certain everything is under 30 inches in reach. In the turntable area...I would leave uncovered and strictly go with buildings on the back-drops. If you want 3D buildings, ensure you can easily remove there should you need to replace a track or work on an issue. The turntable itself is 24 inches. Therefore at a maximum from back-drop to fascia board would be 30 inches--meaning three inches from either side. If you go with your 50 inches in height, you may stand on a step-stool (We have 5 on the Glacier Line) and you will easily reach the back-drop over a turntable.
If you use sectional track, try and not make the track appear geometrically perfect...I'm talking about the "railroadee" thing again. I think the track-work itself would appear more "real" if all the curves weren't exactly the same. I realize that may not be possible but just think about what the curves on the line look like. They are NOT uniform.
I realize that you have an averaged sized area, on the Glacier Line I have curves that are 42, 54, 64, 72, 80, 89, 96 and large smooth flowing flex curves. Do the best you can do. :-) Regardless and most importantly, weather the track and roadbed.
This is going to be a great project. I wish that I lived closer. You did get the book didn't you? I was guessing Thursday?
