The reason you couldn't find them is because they don't have CA51 in the file name. If you look in Sue's screenshot above, you'll see that the 'Dunes CA51' fill references a bitmap called 'Dunes.png'

That's why you can find them using that dialog, but you need to do so from a map in the appropriate style. From there you can find their names, and then in the map you want them in, you can then easily add them once you have learned that filename.

Not much. Mainly a new short chapter describing the Symbols along, fill with symbols, and symbols in area.

Try a fill with a more visible texture. It gets a bit harder to find something nice due to the perspective nature of the map, but you could try with something like the Stone Lava Cooled bitmap from DD3.

Additionally, the pixelation of your current fill is really bad, causing it to appear more like a uniform mess. Try decreasing the scaling of the fill as well. That leads to more repetition when zoomed out of course, so you may need to consider working a bit with the surface, applying layers of different fills and blending them using effects to avoid the repetition.

The symbol behavior is down to you having lots of unrelated stuff on the HEX/SQUARE grid layer. Hex symbols are special symbols that automatically align with the hex grid, but all that other stuff is basically just confusing them.

As for the export, it looks for the lines on the MAP BORDER layer to see what area to export (If you have the restrict to map border option on), and if you check that layer, you'll see that the defining lines (green in your map) just covers the map area, and do not extend to include those informational areas.

Hatch styles are just CC3+ drawings. Very similar to symbol fill, but it uses an .fcw file instead of a symbol. You'll find all the existing ones in @Hatch Styles.

Hatch styles are not normal fills however, and only work with drawing tools. If you make a custom drawing tool, and set the outline to be an extra entity, you can pick the desired hatch style in the properties for it in the tool. The list here is just all the files in @Hatch Styles.

These hatch styles should be basic, simple drawings.

I know Ralf have done some work on hatch styles in some of the live videos. I'll update this post with links if I can identify them.

Here's one explanation: