If you wanted to add some rails and railcars, Remy did a livestream video on drawing rails and railway rolling-stock here, which may be of use.

It's just a thought, but at this large-scale of map, you can use the straight drawing tool and get a nearly identical "natural" appearance, simply by clicking more nodes as you go along. Although this obviously creates more nodes, they'll end up as a mere fraction of what you'd get by always drawing using the fractal tools, which often add far too many nodes on their default settings. You'll also end up with a map that looks pretty well identical to this, but one that you'll have more control over in all manner of ways.

Sue, I think it may be something on the FOREST sheet. I tried a 1024 px export just now, and it hung for a while before rendering the export on that res. It did create the image, however.

Trying to hide everything but the FOREST sheet also had the program hang for almost a minute.

I've found CC3+ will crash (shuts down) without telling you why if you've set the export to a size your system (or the combined your + CC3+ system) can't handle. Occasionally, you might get an error box telling you something similar before this happens, but not always. Typically, I find setting the antialiasing to zero, or just turning it off, will solve the problem. However, it may be there's something else at work in this case too, of course.

You may find too that increasing the line thickness of the grid may help, regardless of what colour you choose for it. The automatic grid creates zero-width lines, which can simply vanish at some image output resolutions.

You also don't have to create a single grid across the entire map. As long as you use the same snap grid point to start your grid's placement, you can have several smaller grids wherever you choose, and they'll all line up OK. That way, you can have different coloured grids on the same sheet (though of course, that may not work for all, dependent on what effects you have on that sheet). Or you can set them up on different sheets to get different effects per grid colour.