I can only second what Scraggs has said. Fantastic piece of kit, takes a lot of patience but the rewards will be stunning when you've mastered it...I haven't yet but, like Scraggs, I've only had it a few weeks.
A ring flash is an essential extra and should be factored in with your spending along with a focus rail.....magnification changes with focus so focus stacking really requires one. My embarassing early trials show that it's easier to use on a crop body than a full frame but this may simply be the "lumpus impatiens" just behind the camera.
I say go for it...we need a few guys groping around with this to start idea swapping.....the dining room table on cold winters nights looks to be the best place.
Bob