For easy ways to place those symbols, either set up a snap grid matching the size of the symbols, or you could probalby get them placed on a line with Symbols Along using the appropriate parameters.

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.