Thank you, Tony; I'm glad this entry has potentially been of use. But you are not lesser mortals; I fear my original decision to start using mock-ups was more likely a product of my own indecision and anxiety! That said, I now wouldn't do it any other way, and the benefits of throwing up simple cardboard models that you can move around along with old bits of track and whatnot far exceeds the "cost" of spending the time doing so. If anything, it's actually quite a nice exercise as it gives you a glimpse of how your finished project may look, and what you could change to make it look that bit better!
Edit:
Here's my previous layout (which I will resume building once Sandy Shores is finished!) circa 2015, with all its mock-ups in place. In fact, I still have most of them in the cupboards in my room ready for when I get around to building the structures!