I'd suggest you keep your costs down and go for a simple solution -- I found Link hidden: Login to view earlier this year and have been using it extensively. It's simple to set up and use, and integrates seamlessly with PayPal.
As far as picking a niche goes, you'll want to put some work and thought into it. Jewelry is an extremely tought niche to get into -- competition is insane. In my experiences with toys, it's better to find a specialty and do everything you can to get known for it. ie. either a certain specific kind of toy (model trains and accessories, etc.) or a certain "meme" to your store (for example all "old fashioned" toys, or all licenced cartoon character stuff, or all plush, or whatever.) Overspecialisation can be a death knell in the offline market, but online it can give you a huge boon as fans of your niche are more likely to bookmark and share if your site seems geared towards their passion.