I generally advise new sellers to seek the advice of a local accountant. Their fee will be well worth the time and aggravation they will save you in setting up your business correctly and advising you on how to apply for the appropriate licenses. You can certainly do this yourself, although a local, experienced accountant may be aware of municipal (local government) issues that could save you time and penalties. You can also consult with an attorney about the appropriate way to set up your business.
One of the advantages of proper licensing, beyond the legal requirements, is the opportunity to buy items at their wholesale cost, or to avoid paying sales tax on items you're not buying at wholesale, but which you will use in the production or selling of your jewelry.
As for your question about selling on your own or through a website like Etsy.com, the clearest advantage to a site like Etsy is their marketing power. They are able to draw more customers and prospects to their pages than an individual seller may be able to. Also, there's a sense of trust the buyer immediately has because the site is well-known and many established jewelry makers sell there.
Those advantages, the start-up and maintenance costs of a website and shopping cart system, along with the professional and peer resources they offer, should be taken into account when you're trying to decide whether to host a site on your own or to become a vendor on Etsy or similar sites.
Other sites to investigate include: Artfire and Artful Home--there are others, these are just the most widely known at this writing.
- Dr. David Weiman