Dave,
You saw my dilemma, (as I knew in the beginning there would be dilemmas), I only have so much space, and I would like to make the most of it. There would have to be major decisions on what to go with, and what to leave out. I have always liked turntables, but I also want some modeled town areas along with mountain scenery! Can one have his cake and eat it too? Possibly not in O gauge in under 144 square feet. 
That is what I asked for lots of ideas. After looking over these plans, I like them a lot. I do intend to run some point to point, but I would also like to do some continuous running too. Continuous run doesn't have to be around in circles. I can run up the mountain, and pretend I am continuing down the other side heading on towards Cumberland. Then a run back up and finally terminate the run. The part of the loop that gets hidden by trees, can represent the mainline going on through, or it can represent the branch line going to Davis. There are a lot of scenarios that can be run here!
As to the passing siding halfway down, I don't know yet. By myself, I may find it too difficult to get two trains to meet properly, like happened on a small layout I had years ago. On the other hand, now that I run command control, I may be able to get it to work. Of course if I had a second operator, then it would be no sweat. Yes, without it it would look more like the scene I sent you in the photo. I will have to find that photo for the group, but not this evening. That doesn't need decided yet.
The staging tracks underneath was a surprise when you added them. I did some measuring, and then setup a couple shelves to test the idea. While I didn't have anything on hand to represent the top shelf that stuck out as far as needed here, I didn't have any problem reaching in to the rear cars. Maybe the farthest in track would be impractical to reach, but overall I like the idea. Again, that doesn't need decided yet, though it would have to be early in construction.
I like the idea of the lift out hatches. With 2-inch thick foam bases and foam scenery, they would weigh very little, and I could hide the visible edges with bushes, etc.
Oh, but I forgot to mention those spurs in the top right corner would be excellent to keep a couple engines parked when not in use. I am so afraid of dropping engines, though it wouldn't be as bad with John's suggested rubber flooring tiles. Still, I have trouble gripping the heavier engines with the arthritis in my thumbs, and by heavier, I don't mean very heavy either. Also, that Lionel engine house could be used representing the one in the Davis photo.
Well folks, what does everyone else think. I do have on 24" turntable on hand, that could be used, but not in these plans. I would like to have one, but they do take up space that could be sceniced.
Thank you everyone who has participated. If I don't respond until late tomorrow, it is because I will be going to the Greenberg show in Monroeville, Pennsylvania. I'm taking a friend who hasn't had trains for years, but he is excited to go. I'm hoping he catches the bug when he sees the Pittsburgh Independent HiRailer's modular layout. It was 15 degrees this morning with wind chill on top of that; snow and ice; but tomorrow morning is to be in the 30s and high up around 50, so I hear.
