Hi, Ian - welcome to the Guild! First, thank you for contributing right from the first post. That alone is worth a smidgen of rep (all I can offer).
Your map: yes, that's going to be a hard set of techniques to blend. The layer-cake topography is neat, but it always makes me think of a physical object, instead of a digital or paper map. Which isn't bad necessarily - I could picture a one-off display piece on the wall of a castle or boardroom, or even a battle-map style table. The ornate ocean could be justified by the map-artifact belonging to a VIP - impress the big shot, we must, or in hot water we may be, yes. So following that scenario, something you do for depicting land cover could be highly detailed. Call it inked or painted on top of those painstakingly shaped layers.
Conversely, if what you have is a "photo of an object" maybe your craftsman-cartographer could have actually stippled the surface - I think I've seen dioramas where that was used to good effect. So your digital depiction of that would be the equivalent of a gazillion little random points, casting shadows like your layers do. Colored green too, just not only color.
The way-thick coast isn't working for me. Doesn't match the ornate ocean, fancy lettering. Plus, dark blue might work better for that and the rivers. When I first zoomed in I was thinking "look at that road running right up a valley. Hmmm, no, it must be a river." You handled tributaries nicely where you put them in, that northernmost river could use more, especially if its size is denoted by the stroke width. Unless it's something like the lower Nile, transiting a desert area?
The wider rivers look like they could use more opacity - they seem washed out compared to the thinner ones. Or maybe the widest ones should be cased - that would make the slightly-translucent color work better mid-channel. What's going on with the river to the NW of Kokojoai on the large island? If you're depicting two outlets to the sea, that's implausible. If you've lurked a while you know about the River Police? I'd hate you to get a citation your first day :-)... Likewise the network on the center southern edge - unless you mean to depict something like the Sudd, along the Nile in Sudan, in which case you'll be wanting to figure some kind of swamp symbology, right?
I like most of your topography - the main thing I'm not buying is the river running the length of the long, flattish peninsula. Actually, the slightly jaggy looong spit of land would best be explained by a mountain spine along it - I'd kind of expect a flattish one to have some obvious sweeps of sandy beach in smooth curves between slightly more resistant rock or earth. See Cape Cod as an example. But it's only the anomalous river that calls attention to its plausibility.
The subtly mottled swaths of color are a good effect, if it weren't for the uniform geometricity of the circle brush you colored it with. Some blurring of those color variations might improve your look.
There's a couple of places where your layers indicate sheer cliffs along a long stretch - is that intentional? Could work, but the way its set up seems iffy.
That seems like a lot of complaints. I'm not pointing out badness, just ways you can maybe improve it -- if it were junk I wouldn't want to pore over it and analyze my reactions, I'd just ignore it :-). I do like what you've got going, and I want to see where you wind up with it. Even some of the bits askew from conventional use might be fine if you work it up right, like the reddish rivers.