Thank you for your feedback, Northern Girl Jewelry! Those are excellent questions.
Sub-categories seem pretty random, because they are based on the users' random replacement behaviour. Those are the exact terms that people use on Google when they replacement for your kind of products. Sometimes materials are included as part of the replacement phrase and sometime colours or audience. We only picked phrases that have a relatively high volume of replacementes behind them. That's why the list is not complete. However, those phrases that we chose are the phrases we want to optimize our product pages for. The terms will be useful to users, as those are the exact terms that will bring them to our site in the first place.
As for the Occasion, choose only things that truly apply to your products. If nothing applies, then don't select anything.
However, I think you could select "Casual wear" and "Dress for Office" for a lot of your products.
I know choosing precise terms that describe your product is a hard work.
But the right terms will bring the right traffic to your store and give your products right exposure on our site. Hope this helps. Thanks!