Looking at some layouts will help you. O gauge has a lot of structures and items for the steam era and the steam to diesel transition. Living the '70's as young man, the cities were mainly '30's to '50's leftovers with only some new construction beginning. Even a lot of rolling was still old and the diesel engines beginning to show refinement.
The forum's publisher Alan Arnold (as leavingtracks forum name), has a large urban layout, Craig and his W & W has urban areas and some elevation changes. The NJ Hi-Railers club has some nice city areas.
I would suggest not to focus on the track plan detail, but instead, the overall design concept. Defining the scenic items will then help with the outcome of the track.
I, too, think folding an oval fits best in your space. I have created just an O72 single main around room for a long passing siding on the inside of the fold. I like getting the elevation in at the elbow of the fold and then overlap the inside and outside in the elbow. I don't get real excited about elevating areas. One can get a similar visual effect with only a 3"-4" elevation of a line at an area. Although, Obsidian and Craig came up with nice design for his W & W South Fork RR.
I am not too concerned about the reach as you have enough space to access the layout from all sides, even if it is a skinny aisle. Access hatches designed in are almost a must have when you'll need to work on scenery. Scenery or buildings can be on top the access hatches, so there's no loss of space.
If you get a track plan that you like, I can save you time by refining the elevations and scenic detail for a good 3D. Those little software techniques will bog down your design process. I have attached your last file with some changes to improve the 3D for visual eye candy. I also changed the max elevation to 7". 4.5" just isn't enough for O gauge. Take a look at the 3D and rotate it around.
