The maps are free for the public to use, so there isn't any real legal or financial damage done if you use the textures. But if you profit from it, then they can come after you.
As far as making your own textures go, it's definitely gotta be your thing or you won't do it right and you'll be pissed that they look like crap. It sounds easy in the tutorials, but if the artist within you doesn't get it, you're in for a rough learning curve. But you need to try it to know....