A few searches would help you here, as these topics have come up before:
Jewelry findings:
https://community.glowforge.com/search?q=findings%20jewelry
Bracelet blanks:
https://community.glowforge.com/search?q=bracelet%20blanks
Cermark brass:
https://community.glowforge.com/search?q=cermark%20brass
Bonus: searching is faster and easier than asking, and we don’t chase our collective tails answering stuff that’s already been posted 
As for copper, you may want to look at #4:
Copper may be dangerous to laser, be careful. You’ll probably also be interested in #11, since it covers a lot of ground about how to work with metals.