I also came from the Nikon D800 and went with two bmcc4ks and two Viltrox NF-M43x, also the 3x K&F Concept...
I've mounted quite some lenses within reasonable steps (with viltrox vs. no-glass) to be ready without having to clumsily switch adapters....
I use eg. Nikkor 20mm 2.8, 60mm 2.8, AF-s 50mm 1.4, 35mm DX 1.8.
besides that, I also went with Meike 16mm and 25mm, and cant wait for the other focal lengths... filming for me is focus pulling with a long throw... well, older nikkon lenses are reasonable long, but far from what the Meike can do...
I also use the Nikon 70-200 with the TC17 to be 340 and then with the K&F, to get 680mm...
or the sigma 150mm 2.8 with K&F, which is still 300mm...
see the long tele lenses in use here:
ONE NOTE: if you have the 24-70 Version I you are good with manually setting the iris, but the newer Version II doesnt have the manual latch anymore, so you are stuck to 2.8 !!!!
regards
Mike