Thanks Harrg! Someone with more technological know-how than me should consider setting up a Discord channel for this sort of thing (or maybe just a CG Discord sub-channel?).
I'm afraid my answer to how polar regions work is rather boring and unsatisfying: I basically just eyeball a topographic map of Earth in an equirectangular projection (I prefer this one from Japan) to get an idea of distortion at the latitudes I'm working at, and then draw my coastlines and topography to reflect the distortion. Once I've made enough progress I upload the map into GPlates for an idea of what it looks like on a sphere, and then adjust the shapes accordingly back in Illustrator. It's definitely an imperfect method and I'm not entirely pleased with how some of my coastlines look near the poles, but I'm not sure what other options there are for vector-based maps. I suppose I could reproject a raster of the map in GProjector, draw the polar areas, re-reproject it, and then trace it in Lightroom, but GProjector only works at up to 7500 x 3750 pixels, while I'm working on a 16000 x 8000 map in Illustrator. At the level of detail I'm working with, that amount of tracing honestly just seems torturous. So for now I'm just doing everything manually, unless anyone has some brilliant technological suggestions.
Thanks Nitro! The "pile of sand" analogy is a good one, and one I'll be thinking about as I refine my topography. I don't love some of my zones where different orogenies meet, but that's a good heuristic to keep in mind, especially when there's no direct Earth analogue I can mimic.
At some point in the future I might try and do detailed bathymetry (as geology, including geology of the ocean floor is rather important for my overall worldbuilding concept), but I'll be honest it sounds nightmarish to me too- drawing mid-ocean ridges is way less intuitive for me than drawing mountain belts. I'll probably just do a basic sketch once I'm happy with my land topography, as that will be a useful guide for determining ocean currents and human settlement patterns, among other things.