I think this may be Remy's blog article you mentioned, Sue. It includes notes on the RGB Matrix Process, at least.

Given the blog article uses an overland example as its RGB Matrix Process test, I'm guessing it will work with that at least (can't be sure if the tree symbols have been affected or not in the blog sample images, however).

A quick test, slapping a greyscale RGB Matrix Process Effect onto one of my own overland maps (whole map setting) suggests it does indeed convert all the symbols to greyscale, while adding a few random choices of dungeon symbols to it, suitably enlarged, shows they too convert to greyscale without problems. Obviously, this is hardly definitive for all possible symbol sets, but it doesn't suggest there's a problem with what I've checked so far.

Actually, any colour version can be readily converted to greyscale simply by applying an appropriate RGB Matrix Process Effect to the whole map, so that would be win-win!

It's pretty much standard practice in a lot of real-world cross-sectional mapping to vary the line direction like this, often to follow a specific passageway, or series of linked passages and caves. The purpose of the cross-section is to provide useful detail that's not so easy to identify on the plan-view map, so any line that works best to show that is appropriate.

Indeed, if you take a look at the PDF mapping guide for CA7, Caves and Caverns, this is exactly what Ralf (I think?) did in drawing the sample cross-section for that cave using the modern cave mapping style.

Sometimes, it may even be helpful to use more than one such cross-section.

Looking at the cross-section on your first map above here, while it's interesting, in pointing out how variable the levels are in different parts of the cave system, it's not all that helpful, since it implies other parts of the caves may be at similarly variant levels, without indicating what those may be.

In some cases this may be of merely academic interest, where caves aren't directly linked to one another and are some considerable horizontal distance apart, for example. However, where the passages and adjoining caves are at different vertical levels, it can be much more important - i.e. if a passage enters in the ceiling of the next cave, say.

It may also be useful to add some cross-sections of individual passage segments next to the area on the main plan view too. For instance, there are a couple of clear choke-points towards the SE end of the narrow, SE passageway. This suggests they're more or less impassable, yet there's a mapped cave beyond them, so there must be a way through, if perhaps only a crawl-space. A cross-section of just the choke-points on that passage next to the narrowest parts would help clarify that.

Now if you only designed fonts as well @Loopysue, there'd be nothing we couldn't ask you for ?

For the size of the Arena, not sure it will help necessarily, but the Greek and Roman stadion/stadium, also known in English as the stade, unit of length was around 180-185 metres in length (there were variants, and some modern estimates have varied still further from this). That might be a way to go, though it would be likely the inner circumference, not the actual length of the construction in an oval form. It really depends what goes on there as to how large it should be.

The River Docks is another in the "length of string" debates, as it depends what the river is used for and by what proportion of the populace, whether it's used for exports and imports (and what of, type and quantities), does a ferry run from here to other places (such as even across the river), etc., etc. To my eye, for a river of this size, the three docks now seem probably too few, but more information would be needed for a more definitive answer, I think.