Johny,
I used the d800 with a cheap samyang 8mm, the one with the removable hood. This is a dx llens but without the hood nearly fills the full frame with the image circle. This allows a single row of shots to include zenith and nadir.
Regarding heads I really haven't got much of an idea, I have a second hand nodal ninja 5 that seems ok.
I'm really not qualified to offer tips on workflow etc. In this I imported raw to lr4, applied some adjustment to shadows sharpening and clarity etc then synced this across the images, export as tiff. Stitched in ptgui without correction. More processing tweaks to the resulting pano, saved as jpeg before outputting with pano2vr, nadir patched in pano2vr to remove tripod.
I have absolutely no idea if this is a decent workflow and tbh I experimented with random sizes for the pano and output trying to balance file size v image quality. It is more by luck than judgement that the results seem ok.