If you want the Mac based machine now, I'd say go for a MacPro for both video editing and rendering. If rendering takes too much, you could add a rendernode to the network using a Windows based PC, 2x4core. 
That Windows box would only be used for batch rendering, so it can do without a fancy graphics card, a $40 regular PCIE x 16 card will suffice, as will a simple monitor.
So it will likely be slightlly more expensive than the MacPro. Much more raw power, less versatile.You could even build the scene/animation on the MacPro, hand off the entire rendering process to the rendernode, and then use the Mac for some video editing while the Vue render controller runs as a modest background process, taking up very few resources from the Mac. 

I suspect the first 2x4 core Mac will be VERY pricey. You're probably better off with a 1x4 core MacPro right now, and expand your render capacity as needed with (relatively) cheap PC boxes.

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