It seems to delete just fine for me without effecting the landmass, so just to clarify:

• When you click to select it, you do click somewhere on that stray part out in the sea right, and not where it overlaps with the landmass? (As that would cause them both to be selected)
• After clicking on it to delete it, but before hitting 'Do It', do the command line reads as 1 entity selected and not 2?

As an addendum, after deleting it, if you want that outline, you can easily add back a correct version by using the change like draw tool command.

But if you are going for a very complex coastline, you may wish to use a glow effect instead of a outline anyway.

1)

Ralf have done both blogs and live streams about creating your own styles. Check out https://www.youtube.com/watch?v=Ni49aWN8wjE and https://rpgmaps.profantasy.com/tag/create-new-style/

2)

Check the list of annuals at https://forum.profantasy.com/discussion/10366/cartographers-annual-all-the-issues-linked-in-one-place/p1 , you may find something that matches there.

3)

You need to set up symbol catalog settings and filters. This is documented in-depth in the symbol management chapter of the tome, as well as in these articles: https://forum.profantasy.com/discussion/7329 and https://forum.profantasy.com/discussion/7338

4)

Roads and rivers use lines in CC3 by default, which always have a fixed width. To make things varied, you can use polygons instead, since this allows you to draw both edges, but it is also much more work. You can also experiment with the displace effect, which may provide you what you need.

5)

Use layers when you need a logical organization, and sheets when you need to either have different effects applied, or need to control ordering in the drawing. Very often, most/all symbols end up on the SYMBOLS sheet, while the layers divide them into things like vegetation, mountains, etc. Think of sheets as things that affects the visuals in the map in some way, while layers are purely logical ordering that can later help you do things like select all the vegetation in the map or things like that.

First of all, always use the metric/m versions of the tools, and not the feet/ft ones as the latter are intended for maps scaled in feet, and produce things that are scaled about 3 times larger.

The hatching will look a bit big, because you are using it on a rather small map. I think this style was designed with the intention that you do full city blocks in one go, not individual sections/houses like you do there.

It is fully possible to edit the hatching to make it smaller though, but it will take a few steps:

1. Start a new instance of CC3+, and open the file @Hatch Styles\CA60 Building.FCW
2. Save it to a new file, like @Hatch Styles\CA60 Building Small.FCW
3. Right click :CC2MOVE: and pick Non Visual Scale. When asked to select entities, hit A to select all, followed by D for do it. For the scale factor, enter 0.5 and for the scale center, enter 0,0
4. Save and close the CC3+ window
5. Back with your map, hit :CC2DRAWTOOLS: and click advanced. Find Building, Hatched in the list and select it (If CC3+ asks you to save settings at this point, say no). Then hit the New button, and name the new tool Building, Hatched Small. We have now created a copy of the original drawing tool.
6. Make sure you have your new tool selected in the list, then click Outline -> Verify that Extra entity is selected and click the properties button there, and change the option under Use Hatch style to your new hatch (CA60 Building Small).
7. Hit OK twice to get back to the main drawing tool dialog, and hit save to save the changes we made to the tool.
8. Now you have a custom tool with half the hatch size.

Changing things like widths of roads and rivers is simpler, because that is just a property of the drawing tool. All you have to do is to make a copy of an existing tool like in step 5 above, and then access BOTH the properties of your new tool, AND the Outline -> Properties and change the width settings there.

Note that drawing tools are system-wide and not map-specific, which is why I always advocate creating copies of tools rather than customize the originals. There's no reset to default button for these, and the ones supplied by PF may also be updated in a patch, invalidating your own changes, so making personal copies is the best overall strategy.

The scale in CC3+ is important, as mapping to scale is what allows you to do things like import a drawing like you have here and scale it accurately.

I recommend having a read of this blog article which talks a lot about the importance of scale:

I recommend starting with the Symbols and Symbol Management chapter in the User Manual (accessible from the help menu), it explains the details of how to create your own symbol catalogs, and then how to import .png's (recommend reading the entire chapter, not just the importing png part inside it, since that part relies on what has been explained earlier.)

The Tome do go into greater detail about your options, but the User Manual should get you started.