For basic proportions and posing I've been using
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, which has a nicely morphable mannequin to work with. Poses I don't really have any specific source of inspiration, although I do try and sketch down any fun ideas when they pop into my head so I can refine them later.
I'd say the biggest step to having your art feel "unique" is to get in the habit of constructing your characters from scratch, even if you're using a pose image as a reference. I'll use Design Doll to get my proportions roughly right and to figure out a few key landmarks (usually the collar bone, hips, and feet contact points), then hide that image and work entirely from primitives from there (there are plenty of great youtube videos on how to do that,
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).
Colouring and shading is it's own beast, and one that I'm still figuring out. For
A Very Full House characters I've got a specific order of operations to it (lay down soft shadows, then soft highlights, then edge light all around and sharp highlights on rounded surfaces. Extra shiny objects might get a pure white highlight added as well.) to help me keep them all feeling stylistically the same. There are a whole bunch of different styles out there; I'd suggest looking at ones you like and trying to figure out what "recipe" they might be using to achieve it: do they use hard light/shadow transitions, or do they blur them? Do they keep their lineart visible? What sorts of colours are they using? Experiment with that a lot (and be prepared for a lot of it to look
bad) and you'll start to figure out how to make things look like you want them to look!
Anyways, I might have given you more than you were looking for
Good luck out there, make cool things!