Great article. Great questions!
The adapter doesn't really help with rolling shutter, but we did not find rolling shutter to be much of an issue. I do think the rolling shutter effect can be amplified when the camera is dealing with more vibration, and keeping several points of contact on the body of the camera (two hands and one eye against an eyepiece) along with a chest brace can help reduce bumps and make the camera feel as though it moves like a heavier camera that would sit on the shoulder.
We shot with the Metabones Speedbooster adapter that is designed for the BMPCC, and it basically squeezes a super 35mm image onto the cameras super 16mm size sensor. Because of this, the field of view on the Nikons we shot with were comparable to a lot of other 35mm sensor size cameras we've used.
We shot with Light Craft Workshop Variable NDs. Those were just what we had (we didn't do any testing) and they worked out fine for us.
When you're shooting with the Metabones Speedbooster that is designed for the BMPCC you end up squeezing nearly a Super 35mm image onto the Super 16mm sensor, so there isn't really a crop factor to deal with. Our widest lens was a 20mm, which had a wide enough field of view for what we were doing.
Danny and I weren't directing the film, so we let Diego focus more on performance. Diego was very aware of how we were covering the scenes even though he didn't have a director's monitor, and we did watch playback from time to time, but not as a rule.