As others said AF with the AF-ON technique is a standard today in macro photography. But manual focusing in addition to the AF is for some situation superior. I have the Subal 105 manual focus flat port which has a built-in crone for manual focusing on the Nikkor 105.
The manual method lets you focus exactly on a specific part of the object e.g. the eye of the critter without shifting the camera (focus and recompose) or selecting different focus points in the viewfinder. But this also has some disadvantages, e.g. you must use both hands (left hand to manual focus and right hand to release the shutter).
Manual focusing also requires a bright viewfinder of the camera (with a fast 2.8 lens as the 105) and preferably a housing viewfinder (45 degree viewfinder from Subal and others or GS180).
With AF and assuming your rig is well balanced (neutral buoyancy and also not forward or backward leaning) you can use one hand (the right hand) only for focusing pressing the AF-ON with your thumb and release the shutter with your finger while holding on to something (but not a coral!) and thus stabilizing your position with the left hand. I also like to use one of these "Lembeh sticks" for stabilizing.
bulkhead and internal HDMI cables (within camera housing): 100 (approximate, not measured)
total additional: 528
grand total approx. 2.2 kg
If Nauticam speaks of around 1.0 Kg then it is only the ninja housing, I guess.
To counterbalance the additional weight (and some of the negative buoyancy I had before already on my setup) i have added 2 of the new Nauticams' carbon arm floats. Each of them give me around 250 g of a lift underwater.
I also have a D4 and the actual recorded stream is 1080p at xxx Mbps for ProRes and/or DNxHD codex (measured) even when cards are inside the camera (but no video recording through the camera). I guess this is the same with a D800, but why not asking your local Nikon rep?
I believe the specified weight of around 1.6 kg on air includes the ninja with 2 batteries and the HD/SSD disk inside (but I will wight it tonight to be fully sure).
The handling with the sun shade underwater is quite ok since all the important functions (start/stop, zebra, fals color etc.) are on the right side / inside the sun shade. I usually press the respective buttons with my thumb of the right hand while holding against from behind the housing with the rest of my right hand. Start/stop button is most important to operate underwater and this is at the lower right hand corner which is the easiest to reach