The atlas is at https://atlas.monsen.cc

Generally, the amount of reserved areas compared to the number of maps is quite low, so finding one is actually difficult, but if there are any reserved areas on the current map, there will be a button below it named "Show reserved areas". That that button does is just to enable reserved ares to show up with a hotspot just as the existing areas, meaning every hotspot marked on the map leads to either an existing map, or a place someone has reserved, while a non-marked area of the map is open for the taking.

You're probably planning to fix it already, but that farmland cutoff at the top looks a bit artificial being so straight and all. A few trees covering up parts of the edge helps a lot here.

Reducing the scale of a single fill is just a matter of opening up the fill style dialog, selecting the appropriate fill, and reduce the width/height values.

Farmland fill looks a bit too large scaled IMHO for that small island. Have you tried reducing the fill scale a bit?

That's easy enough. When you build it, it creates a .dll file. Just give people a copy of this file and tell them to put it in the CC3+ installation directory (Just make sure you build it in Visual Studio using the Release profile and not the Debug one). I am pretty sure people won't need to install any C++ runtimes.