Parametric sphere array along concentric circles

Hello,

I'm still new to Grasshopper so I might have bit off more than I can chew on this one.  

I'm trying to array spheres along concentric circles.  Each of the circles are raised along the z-axis according to an expression, so that the entire structure resembles a cone.  I'd also like to build in a "twist" parameter so that innermost circle rotates, and the remaining outer circles follow in spiral.    

I initially started modeling this by ArrayCurving the spheres along a spiral in Rhino, but I couldn't get the top and bottom of the spiral to end in complete circles and I wanted a little more parametric control over the entire structure.

Here's what I've got so far.  Any help would be much appreciated!