Bob: Glad you are reconsidering shelve widths. I set up some test shelves just to see what I could reach. Found that for me 28" is good. My 1st level is 36" from floor, 2nd is 56". I chose the 20" rise as the middle blob of the layout is more or less transition between the two levels and there are spots where RoW has another RoW 8" above/below. I am not fully sure that I can pack the transitions in 28" shelves and have it not look like spaghetti. Time will tell on that one.
Helix: Since I have room, I decided on a oval type. I am setting it up with staging, so the inside track is 30", - heck, pix is worth a 1000 words:
View attachment 171186
This is Open Office - L2L is one loop. I don't know where else you could put 25 staged trains in ~52 square feet. I did play with this making the Separation 5" with 4 Levels, but that got the Grade above 1.5% which probably would work, I just wanted to stay on the safe side.
Block Detection: This looks to be pretty simple. Current detectors on each Main/Branch block and Control Point, with IR emitters/detectors in each Control Point turnout. Means that every train has an EoT device or rear power. I want more or less real signaling - CTC over APB for the mains, ABS for the branch lines. I have started to break up the track plan with 22ft minimum sidings and intermediate blocks. If I remember correctly, I have 8 sidings on the Main, and have not set up any so far on the Branch lines. So that is 16 Control points on the Main, and at least 64 signal heads; not including any Advance aspects. Aspects for this railroad are pretty much what the 1:1 does in this area: Red, Yellow, Flashing Yellow, Green and Dark. I have not found anything to buy off the shelve that does what I want and from what I have seen so far are $$$. So I am the process of rolling my own using Atmel/Microchip devices. I did look at Arduino's which are cheap, and since I would have to write code anyhow, went with Atmel/Microchip as they have more options with internal workings.
Turnout Control: I have decided that only Main and Branches have remote control. Any yard/house/industrial tracks can be operated lineside. I bought a bunch of Tortoise machines years ago and thought them spendy at that time. Now days - geesh. Have been looking at servo's for doing the control - much much cheaper. Most have 'limit' switches/points that can be used for turnout position so those may work good.
This stuff will keep you busy for *years* - have fun!
Later