Hmm, a lot of it is an unconscious collective of my years of digital painting experience, so it's a bit difficult to put into words but if I had to say,
1.) Get a good reference image. I do all of my paintings from photo reference so I don't usually invent light sources, just reinterpret what's already in the photo. I find the most effective ones to be pictures with strong directional lighting with distinct shadow shapes
2.) Learn the underlying anatomy of cats. Understanding the actual shapes that make up a cat allows you to recognize the how and why the shadows and highlights in the reference image work the way they do.
3.) The way I do fur is I get all of my colors and shading down and as final step go over certain areas with a textured blending brush, following the contour of the fur. (I use my own custom brushes in Rebelle 7 but I believe other programs have similar 'mixer brush'-like tools)
I also recommend petting your cat to get a tactile feeling of the planes of her face, what direction the fur goes in where. What kind of movements would disrupt the direction?
As for color-picking I usually go into photoshop and mess with the lighting and color adjustments until I get something similar that I'd like in the final painting.
Then I filter > noise > median to get rid of a lot of the details so I'm left with mostly blocks of color and color pick from there. idk if other programs have this specific blur type, but your standard gaussian blur works just as well
In my experience, when you do a lot of painting you eventually are able to see colors in areas of photos that aren't technically captured by the camera but could be perceived by the eye in real life. For starters you can focus on adding more saturated colors in areas of shadow or plane changes.
If you add a color in one part of the fur try and have it, or a similar color, in at least another part of the fur so it looks like more of a cohesive image.
As for other resources I never really did any specific studying for drawing cats in-particular, it was just something I started for fun and honestly haven't really been able to find many resources on it I found super useful.
If you (or anyone!) has any pieces they'd like me to look over and give direct feedback on I'd be happy to help! Might be a bit more useful then trying to verbalize the specific painting neurons that possess me whenever I'm working on a piece. :)