Mark:
Whatever you do, I would recommend that you stay completely away from 24 inch wide aisleways--way too narrow. Fine for access but terrible when more than one person is there. Bad for viewing as well. 30 is the bare-bone, but I do understand that there is ONLY "x" amount of space. Compromise is always required.
I certainly appreciate what you are sayong about handling engines and rolling stock. We "fiddle" ours rountinely and have broken off more pieces than I can recall. We attempt to only fiddle cars that have less easier to break off parts. You really struck a chord with me when you wrote of a 4-8-4 premier steamer. I just managed to break off my connector between engine and tender yesterday! Up to Mr. Muffins come Saturday.
Since you have been blessed with this "extra" space I would seriously focus on YOUR primary wants and wishes for this layout. What are the most important elements of the layout. What can you not live without?
Here is a random thought, how much do you "gain" by having that yard? I can tell you firsthand, you will NEVER have enough space on any model railroad to store all your rolling stock. I have an entire basement and my yard lanes and storage lanes are not nearly long enough or large enough. That is why we have shelves that hold 300 cars and I'm about to add my shelves. Yes, I'm nuts and addicted I know. LOL
I absolutely LOVE the loop to loop main line following the walls because it makes good use opf the space. As far as the yard placement I just don't know if it's worth the space it takes. AND, I'm looking at the track arrangement of this yard. My question to you is WHY are the tracks arranged in this manner? Are they patterned after reality? Set up that way for a specific purpose? Or just drawn to fit the space?
Last thought, because I've typed way too much already, an option to a yard and a huge space saver...I hope that I can explain this clearly enough....build staging "cassettes" that hold about four to six cars (I'm guessing that you will run shorter trains to make the layout appear larger than it is) and store them beneath the benchwork, yet make them easily accessible. Have one area on your layout--a siding--off the main where you can either "drop-in" or "lift-out" a cassette to "fiddle" cars on and off the layout.
The cassettes could be built with handles making it easier to handle and not touch rolling stock. It would be easy enough to attach wires with male and female plug connectors to power the cassette lift-out set-in area. Believe me, you could store a heck of a lot more cars under that layout than you could ever put in that centered yard--which may require using narrow aisleways and affect the asthetic appearance of the overall layout.
What are your main priorities and goals?
