Snader is right. As a baby step right now, make bigger cracks. Right now, the sizes are all uniform. As well, make sure you're looking at reference. Jessica Dinh's stuff is a good place to start.
Yeah. Do not depend on filters and renderers to do these textures for a while. Use of real world texture overlays are fine, but you need to endeavor to good painting right now before we can add in the extras. Or else, we run into the issue of allowing our computer-calculated art to carry most of the strength of a texture.
Not. It's a very obvious copy of this: and is only about learning to paint materials, not tiling textures. That said, It would be a good idea to work with a square texture and make it at least somewhat tilable. Doesn't have to be pixel perfect at the edges at first, but it will teach you how to spread out your detail and…