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I fear I may have tried to do too much all at once, without fully absorbing the lessons before moving on.
I know that feel. It might be boring and take a while, especially when you're chomping at the bit to get going with a project, but it pays dividends to first watch/read a guide all the way through, ideally making note of the places where the most pertinent information is located for future reference. But, of course, it's easy to forget to do that in the heat of the moment, as many (yours truly included) can attest.
UDIMs aren't too difficult, the guides by Styl1sh have all the info needed to get them set up properly, but there are some odd pitfalls that you need to watch out for. You'll need to save the UDIM textures to a file immediately, for example, as they aren't saved into a blender project save for some reason. Lost quite a bit of work thanks to that, let me tell ya.
She still has some spots that could use a second pass, the arms and thighs (especially around the buttocks) most notably, but it's coming along nicely.