We recommend adding plenty of supports in delicate areas - it's easy to remove a small strut after casting, but it's hard to repair a complex wax that has crumbled. It's really expensive, and you say the waxes aren't as good as hand carved ones. The current state of prototyping technology is certainly not a universal solution, and there are many cases where it makes more sense to carve or build your object by hand. No, we can only build from a 3D CAD file. If you need help developing one, we may be able to refer you to a CAD modeling expert who can help you develop it.
People use Rhino for building everything from jewelry to boats.
There is a free 30-day demo at the site, and also an excellent support newsgroup which can answer any questions you may have. Two programs targeted specifically at making jewelry are JewelCAD and GemVision's, Digital Goldsmith Matrix , which is superb for building rings. These are far more expensive than Rhinoceros, but if you're making jewelry they will have you in production much quicker than a general-purpose tool. Solidworks is a popular general-purpose modeler that is also in a higher price bracket. All these are commercial PC programs.