These lines happens because nodes are placed in such a way that you get very sharp angles on wide lines. There are two main things that can be done:

• Use the SIMPLIFY command. This command removes nodes that are too close together, and might fix the problem. One needs to experiment a bit with the simplification distance to find the best value, as this depends on map size. For larger maps, it may be 1 or more, but for smaller maps, it may just be a small fraction. Save your map before experimenting so you can easily go back to a previous version (Undo also works)
• Stop using entities with a separate outline entity, and use effects instead. Since this problem is connected to wide lines, it doesn't affect the landmass itself, only the outline that has been applied. For example, on the Mike Schley overland, this outline is on the COASTLINE sheet. Hide this sheet, and apply an outer glow to the land instead.

That's generally a good approach. The most important for people reading your story is to identify the places they read about on the map. Then you can expand on it later with more names if you write more stories set in that location.

The ".png.bmp" filename is part of the process. If you see a file with this ending, it basically just means the export crashed halfway through.

Basically, what happens is that CC3+ needs to render the entire map before it can be converted to png, it cannot simply be exported straight to png or jpg, and the native format of windows is BMP. So what it does is that it always exports the file to .bmp first (this is the map.png.bmp file), and then at the end converts it to png (or jpeg) which results in a new file, map.png, and then the original bitmap file (map.png.bmp) is deleted. But if this file is still around, it usually means CC3+ crashed during the export so it never got to the conversion and deletion steps.

Do the crash only happens when you go up to 9000x9000? I see you mention 6000x6000 being to small, so I assume that one actually exported?

This is an issue with the old FT3 that is fixed in the newer FT 3.5.

The issue is that FT3 saves its settings in the program directory, which windows only allows if you run the program as administrator (Right click the shortcut -> Run as administrator)

By default, templates only contain references to the fills used for the style (You REALLY don't want to have them all listed, trust me :)), so that means that drawing tools not made for the current map style will show up using the currently selected fill (see your status bar), instead of the actual fill used by that tool in it's native environment. (Your current map seems to be the Ancient Tombs style)

There's more information in this FAQ topic, including how to import the fills to the current template: