I defiantly agree with all your advice; especially with the light source. I did this with a large amount of influence from an easy to find fox reference photograph. I couldn’t see the direction of the light clearly in the photo so I kinda hoped it would come out of the process (it clearly really didn’t). I was wondering if it would be better to, after I finished the outline, create my own light source and go by intuition after that.
It's important to like the grind of pixeling as a pixel artist. It looks good. There are some readability isssues in some areas. Add better placement of shadows and highlights, this will help fix that. Currently, there is no light source. Imagine a light source in one direction of the fox, then place your shadows and highlights according to that light source. Also, I can see the letter "K" in one of the brown spots on the fox. I hope this helps. Welcome to PJ.
Yes, that can work. It's your work of art after all. However, the best way to learn is through trial and error. Try not to overthink and start simple while progressively adding more details. Start out with one flat color, then add the shadows, and then the highlights. Or highlights then shadows. Highlights pointing towards the light source, shadows pointing away. Shape and depth of the shading will come naturally as you work to make it look right.
Remember to link the refrence if you heavily use it.