Hi there,
I guess the first question I would ask you would be what is your experience in general with 3D modelling? Experience in jewellery modelling?
There is quite a difference between creative 3D modelling and industry specific plugins.
Plugins such as Rhino Gold automate/simplify and enable jewellery specific functions to be used within Rhino. There are libraries, tools for gems, pave, ring sizing etc etc. You can use presets and create your own. In saying this, without knowledge of jewellery manufacturing and also traditional bench work I feel these types of plugins can only take one so far. Also, being that plugins are just that, plugins into a main piece of software, you need knowledge of the software to really utilise all functionality. ZBrush and Rhino are essentially incomparable. Together they are a powerful combination. ZBrush has a very steep learning curve. For accuracy and precision you cannot go past Rhino. ZBrush is best used with a Wacom or similar. Think of ZBrush as sculpting/freeform…think of Rhino as precision and incredible surface control. T-Splines is also a great companion for Rhino and ZBrush.