Haven't tried Poser in a long time. But one of the liabilities back then was that the joints were funky, like they would bulge too much when bent. Also they didn't have very good articulation in those places. I don't know whether that's still an issue. But artists using them as models do have to clean it up, especially in those areas. The ones who didn't would be easily seen to be done in Poser.
The good news is that one has a model at all. And with all the improvements in 3D it's getting to where one doesn't have to do all that much. Of course if one is doing the kind of style you're doing, it's easy to hide that as the source.
So this is why it's a good idea to learn the basics of anatomy so that one can fix anything from a weird area to moving things around and still make them seem natural and fitting with the rest of the pic.
Very nice ideas. You have gotten the mood just right. Not sure why you would want to never use a gradient tool because they can be used for so many things besides a straight opaque fill. One can use it for lighting when using blend modes and so on, just as one place they are beneficial. If it's transparent enough, it becomes a tweak rather than something dominant.
As to what you might focus on to really bring your models up, you might want to study two art teachers from the era of those book covers: Frank Reilly and Andrew Loomis. You've probably heard of Loomis, but Reilly had also systematized his palettes and might make your color easier. He pre-mixed the flesh tones in something like a 10 step gradation, and then it was merely a matter of matching values. And clothes would be like 3 steps, hair about 4 steps. And you would do well to think in terms of planes, particularly in the face. It will shape your characters in a much more credible way and you can get into more subtleties of expression and features.
By the way, your backgrounds are just right, and the overall look is perfect.
Go man go!!!!!!














"Not a bit is wasted and the best is yet to come. . ." -- remembered from a dream