Generally, I would suggest trying out different brushes and see what works best for you, and if you're looking for info (tutorials, advice, or both) about how to draw or paint certain things, I recommend looking up tutorials on YouTube. Same thing applies to Nomad Sculpt functions and 3D models ^^

Hi! As for technical info, on Procreate, brush sizes are determined by the percentage of the total size of the canvas — not by set pixel sizes. Also, I would suggest trying out "multiply" layers for shadows and "add" layers for light and light effects within Procreate as well