Sewing is all about baby steps. If you have other friends that belly dance don't be afraid to ask them if you can look at the way their costumes are put together. Look at the inside. Check out the fasteners. You can learn a lot that way.
Find a good basic sewing reference book. Used bookstores often have them. In a pinch you can get one from the library. Before you cut into expensive fabric you can do a test garment out of old sheets, muslin, yard sale fabric or clothing you no longer want. Baste it all together and then when it fits right, carefully undo the basting and you'll have a pattern that fits you. Try to find a sewing buddy so you can measure and fit the tricky spots where you can't reach. Sewing is fun in small doses so you don't get frustrated. When you quit for the day, quit after you've had a successful bit of sewing. That way you'll look forward to getting back to it.