Can you have more than one enchantment on a piece of jewelry? Yes. Should you have like many many many of them on the one piece? You could but it isn't recommended.
You should always limit the number of enchantments if they aren't somehow related. Like love, beauty and happiness could all go together. Prosperity and good luck could go together easily. However, you wouldn't want to enchant one item with protection, beauty, love, good luck and balance for your life...you get the point, right?
A charm bracelet, however, can allow you to enchant several pieces each for a different purpose. I had one that I did like this years ago. Worked out real well.
And of course, before you try to enchant a piece of jewelry, you need to study about magick. You need to master all the basics before taking on any enchanting of items or casting spells. Otherwise, you wont have a clue as to what you are doing or how it works.