The wave fill is defined in each template, so you'll need to edit it for every map you want it changed in, but what you can do is to go to Symbols menu -> Symbol Manager, then check the box that says display fill style symbols. You should now find the Wave fill symbol in the list. Select it, and hit edit. Define the two corners of the editing window as CC3+ asks you to do, and then simply use :CC2MCHANGE: on the waves and make them black. Close the editing Window, and say yes to keep the changes.

Well, if you just want to use that zoomed-in portion as it is, then all you have to do is to use pick Rectangular section JPG when you save the map, this causes CC3+ to prompt you for two opposite corners that define your export area instead of exporting the entire map, this allows you to export arbitrary (rectangular) portions of it.

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.

Change the display quality using :CC2RESMODE:. Set it to Fixed - High or very high. After doing that, you can try setting it back to automatic and clearing the bitmap cache, but if the issue remains, just leave it at fixed.

CC3+ uses 4 different resolutions for performance reasons, and what you see here is one of the lower texture resolutions being displayed instead of the higher one that probably should have been displayed in that situation.

Note that "Sample size" is just the size of the sample window, it doesn't affect the drawing.