I know Bikesource sells Kuat. I bought my Sherpa from there. I think REI carries them as well. Cannot comment on the 4 bike rack system. That's only available on the NV. 

I have had two bikes on the Sherpa with no rubbing/contact issues. They alternate which way the bikes face to keep handlebars and pedals from falling in line and contacting each other. I would assume the 4 bike system works pretty well. Kuat's engineering seems pretty well thought out. 

::EDIT::   

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Looks like there's only 19 5/8" (~500 mm) spacing between bikes facing the same direction. So assuming identical bikes (i.e. handlebars line up exactly) you could end up with two sets of handlebars trying to occupy the same real estate.