The broken-open eggs could use a more ragged broken edge. They look much too neat presently. And again, sorry Sue!

That's fine. Didn't realise the gallery map might be different to what you'd posted here, and assumed the close-ups were from the final version.

Technically, it's not simply the colour, it's the effects on the sheets involved as well, but it happens when identically-coloured pixels overlap one another, if I've understood it correctly.

If changing the colour doesn't solve it, you can alternatively try copying the text to a new sheet with no effects on it, either above or below the current text sheet, but above whatever sheet is causing the interference (i.e. the contours sheet here, probably). I've found sometimes this works only in one configuration, then in another map, only in a different one. No idea why, as it's not happened all that often.

If you're struggling to work out the general sizes of things as a whole, you might find it useful to look through some real-world maps, like an atlas, a map of your local area and your own town, for instance. That should give you some ideas about the amount of detail visible on different area-sizes of map.

It might help you too to draw out some sketch-maps by-hand first of what you're wanting to create in CC3+, as that way you can get a rough idea of what size of map is going to better-fit the map you're wanting to draw once you start-up in the program. Even if you don't get it right this way, you can always resize the map in CC3+ if you find the area's too large, or not large enough. We've all been there!

Not sure I've ever used the Blend mode, so am pleased Sue's already jumped in on that one.

The three brown areas do have a very sharp line across where the sandy lower cavern floor cuts across them, which I assumed would be addressed later on. The downside with work-in-progress topics is I'm often not clear which items are more nearly finished in them.

I'm guessing it's the general disconnect that you're finding problematic, with that darker piece each as well as the sharp dividing line where they overlie the sandy lower cavern area. Presumably, that wasn't what you wanted there. So you need to identify what the three areas are meant to be and where they are in relation to everything else nearby (higher or lower, or simply a different floor texture, say). That might give us some better ideas what to suggest to help.

Live & learn, Jim...

You might find it useful to see this PF blog posting from a few years ago. Although it's dealing with creating battlemaps from a larger dungeon map, it does have relevance for what you've been trying to do here, I think. Only chanced-upon it yesterday myself, because one of the author's random-design products was the "Deal of the Day" on DriveThru RPG, and I was hunting around for more information, because he's made very extensive use of CC3+ in mapping for his products!