With Premiere Pro and that setup, you will need to render the timeline after making changes to grading, or after adding transitions like cross dissolves. Takes couple minutes per minute of timeline.And that 500gb drive will fill up pretty fast!
But otherwise, the 760 card will make the 4K camera files flow quite nicely. Best practice is delay adding transitions or grading until you've got the cut basically figured out and blocked. That will minimize the need to render. Then as the last steps add grading and transitions. Or you can add the transitions as you go, but keep them turned off.
With Premiere there's not much reason to proxy edit those 4K files. That will just take up more space on the small drive. On the quad "monitors" set the scale to 25%, which will make the 4K image fit in the monitor, and set the quality to 1/4 or 1/2, which still looks great.
The quality of the 100mbps, Quad HD clips from the GH4 is no joke. I watched 35mm, VistaVision, and 65mm, and Imax dailies throughout my working career. When lighting, exposure, and focus are correct, what I see coming out of the GH4 in Quad HD at 29.97P is in that quality league. Don't get hung up on the numbers, go by what you see on the screen.
PS, use Cinelike D for maximum dynamic range, but keep all the parameters at zero for best quality. All the "-5" parameter recommendations you see floating around just leads to clips that can't be properly graded, and that look like mediocre release prints dimly projected at the 48-plex.