Re, those S-curves: Connecting curves that turn in opposite directions directly end-to-end is almost a guaranteed spot for derailments, although you might get away with them at very slow speeds. Author Paul Mallery (old school track and bridge expert, and author of at least three books on those subjects) opined an acceptable alternative is to insert a length of straight track in between circular curves. He suggests a length equal to the longest equipment you plan to run.
You have obviously taken this to heart already, as you had several of those problem areas in your first plan, but seem to have fixed them in the second plan. Your friend did give you good advice and you took it. Well done.
As others have said, I'm curious too to see how your layout build turns out.
------
Re, the N-scale stuff: You don't have to give it up entirely, just because your focus has moved back to HO. You could build a module or two and run them as part of the DeNTrak group:
You may already have seen these guys at shows along the Colorado front range (The Rocky Mountain Train show in Denver, for example, which had a big turnout after a couple years off due to Covid). Good group of gents, IMO, the DeNTrak folks.
The NTrak module height is 40," which is good for shorter people...some aged less than seven, others well over seventy...and everyone in between....
While NTrak does not use Kato track, it's not very hard to lay straight track on cork roadbed--if you can build the track plan you have laid out above, I'm sure you could handle it.
The modules use a short track connector, one module to the next, plus a few common bus wires and plugs. Once again, if you can build that ^^^,
nothing about NTrak should be insurmountable.