I second what Tommy has said about the sculpting challenge, once you get that challenge done you can sculpt anything for free including metal.
As for the traits thing, if you do a poor job parenting then the trait should be chosen for you. But if you have a YA with only 4 traits of any kind, then that's a bug. I know Pam and I have both experienced this, I'm sure others have too. When the bug happens, you choose a trait at the appropriate time, but then for some reason the trait doesn't show up. Resetting doesn't fix it. The only thing that does (and sometimes it doesn't work) is to go into testingcheatsenabled true, shift click on the sim in question, go into change traits, and then add the trait you want that's missing. You can also change any traits, but obviously that would be going against all kinds of rules! It's up to Metro to decide if he'll allow this use of a cheat to fix the problem, but that's the only way I know of to fix it.