The crispy lines are a problem that I had too. I tried sanding them out at first, but finally just lived with them. You can kind of see them in the final pewter casting before I painted it. The trick is to use several of coats of enamel paint until they build up enough to hide the lines.
I haven’t run into any gold/copper colored low temperature alloys yet. And these silicon molds are only for low temps (<650F I think). I made a King of Random (He’s on YouTube) metal foundry for aluminum and brass, but I haven’t had any luck casting anything this intricate with either of those metals.
So for now I’m stuck with silver coloring on my pins.