Not sure why the tools are identical. Might be just to allow for different filters to match, i.e bot Terrain ad Vegetation.

I don't think any belongs on a different sheet. both are background polygons, and there are no other sheet where they would fit in as far as I can see. I thought about the vegetation sheet, but then they would end up overlapping things in a weird manner, so I don't think so.

Correct.

You could edit the template behind the maps instead, that would affect all future maps made from that template, but not existing maps.

Seems to be an error with the .symfill files themselves. I've alerted the appropriate individuals.

One way you could approach it is to decide the size of the average house. A medieval or earlier house for commoners were usually a tiny affair, often no bigger than my living room. Then, based on your house size, so you can used that against the sketch to determine size.

Lurkers are always welcome too, but don't hesitate to jump in if you have any questions or a map to show off or get criticism on.