Steve
I've opened the track plan you posted at the XtrkCad group with XtrkCad. The good news is that there are only 2 places with red track - a minimum radius violation or similar - and these are not on the main line.
The bad news - and I'm being my blunt, negative self here - is that if you use this plan, you will spend a couple of thousand in construction. Then you will abandon the layout, tear it down, or give up the hobby. I know you are set on the plan, but it's not a feasible plan except for the most dedicated, non-handicapped model railroaders I can think of.
When I was 10, my father and I built a 6ft x 13ft HO layout against the wall (13ft side). We put in a couple of access hatches to build and maintain the track near the wall. Even as a healthy pre-teen, I grew to hate ducking under to get to those access hatches. The back tracks were neglected because nobody wanted to use the access hatch on a regular basis, and the layout became more and more dysfunctional. After about a year it was abandoned (without any scenery), and a year later boxed in when we moved overseas. When we returned to the house 3 years later, the layout went into the dumpster without any regrets.
When my father retired, he built a large donut shape with an extension for a yard. He was in the middle of the wiring when he injured his back and shoulders. Even though I offered to finish the wiring for him, he refused and gave up all but the yard because the ducking under was too painful. After a year or so, he just built structures because the main line didn't function well enough to move trains in and out of the yard. Two years later, he gave up the hobby completely.
I tell these stories because they are true, and because you are headed down the same road. You rightly rejected an around-the-walls plan because of your disability. That same disability is going to make those access holes very painful to use on a regular basis. Similarly, wiring underneath the layout is going to be a challenge for you. I don't know about you, but for me model railroading is an enjoyable hobby. That means the tolerable pain thresholds are lower than for normal life. In real life, I have to deal with unpleasantness as it comes my way. In my hobby, I don't unless I choose to.
Another take-away is that the access holes in the lower part of the plan are 6 ft apart, which means a difficult 3ft reach. Given your disability, what is your real reach across a layout of planned height? How long can you sustain that reach? Do you need to sit often, or most of the time? What is the long term prognosis for your back - is it stable, or will it likely deteriorate further?
There are plenty of model railroaders with disabilities - but their techniques, materials, and layout plan are adapted to not conflict with their disability.
The easiest way to fix your layout is pull it out from the walls to create a back aisle, and shrink the plan as necessary. Other possible directions include switching to N or 3 rail O, or picking a theme that can use 18" radius curves in HO (what I do).
Or change the layout configuration to conform to a height, wiring and under layout installations, and reach that suit you. I would suspect that you would be much happier with an 18" deep shelf against the wall, at a height that suits you. Wiring would be on a shelf beneath the "track shelf" and brought to the front as much as possible. A swing gate would be a lot more usable than the access hatches, and could give you a nice continuous run.
just some thoughts and suggestions - ultimately you decide.