I love Blender...
...and as it develops more and more I have to pinch myself. Isn't this something I have used in Maya already? Or is it something that I used first in Blender? UDIMS are one of those things I cannot remember which software package I used them in first.
If you don't know, UDIMs are a way to allow you to have more texture space and multiple texture sizes on a model so you can add detail where you need it and use less where you don't. The sole of a boot? Not as important as the skin of a face, right? Well, that depends on whether the boot is hitting your full frame and the face is all the way back from it, but you know what I mean.
So your UV grid goes from 0-1, 1-2, 2-3 and so on both horizontally and vertically, right? Well, each of these square blocks has a number value which in turn can be added to your images so a colour map can have a bunch of images across a body, so one for an arm, one for a leg and so on... Naming conventions are like this:
figure_colour.1001.png - this could be the Body UVs,
figure_colour.1002.png - this could be the left arm UVs,
figure_colour.1003.png - this could be the right arm UVs
...and so on. Rather than jamming all of your UV's into a single 8K tile, you can spread it over 4 2k tiles. It's more efficient. And it's so cool to use.
Right, enough of this, take a look at the tutorial. It's not a long one and hopefully shows you what I'm trying to explain here.
Take care, guys!