Answering the first question as I have no experiece with Krita, if you can create clean artwork with a good sense of anatomy, I deem that good enough. Watch Aaron Blaise and Devin Elle Kurtz on Youtube and their livestreams, and watch closely how to use layers for shading, light, etc. and use shapes and reference to create subjects. I reccomend taking notes all the time.
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Devin has a video of how you can draw anything here. o
To learn or research Krita, look up guides, tutorials, and videos, those always help with drawing programs. Also go to their website and learn about features, etc.
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Edit: Fixed link.
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