One thing I use layers for is to simultaneously reveal or hide things that because of different sheet effects need to be on different sheets. I once designed a five-level sewer system with each level of the sewers involving multiple sheets on a single layer for each level. Or a mountaintop covering a dungeon that can be hidden or revealed with a single layer.

There probably are in some of the top-down dungeon sets, but there aren't as many symbols available in the Perspectives style.

This is really lovely. My only ever-so-slight feedback is that my old eyes are finding it a little difficult to read the legend, so I would consider increasing the opacity of the background fill/color slightly.

This is a different approach than what you’re asking about, but possibly with the same end result: Remy did two tutorials showing how to construct rail tracks: Martian Mines and the Silver Mine.

Yes, I did use the draw tools for the trees - worked great! For the river, I used "Change like draw tool" to change it to the 75-foot river. I also used the "Change like draw tool" for the sea (the straight closed polygon water tool), the three main roads, the round towers, the square gatehouse towers, the docks, the parks, and the buildings. I used the draw tools (but not the "Change like draw tools") for the city walls, the bridges, the trees, the darker grass beneath the trees directly to the south-east of the castle, the fields, the hedges, the dirt roads, the town square, and the forest on the north side of the map. For the heraldic symbol, I did as you advised, moving the components to the appropriate sheets and changing to a solid color. (Interestingly, the deer didn't fill in completely, just the outline.)

There were some minor issues that had to do with how Watabou exported the data. The river was in multiple sections, broken by the bridges, and the stretch between the final bridge and the sea wasn't there at all, so I did that part using the draw tools. The major road coming in from the west continued up the river a bit, so I had to trim off that part. Same with the road coming in from the south: it continued down the river from where I put the wooden bridge. So you just have to pay attention to what's being changed to make sure the right things are being changed properly, knowing that you might have to trim a bit here and there, or use the drawing tools to add a bit.

But overall, worked great! I am going to do a larger town now, and will time it to see how long it takes.