Adding my few cents to the card and battery discussion.
The Nikon Df has significant space restrictions, which lead to the fact that it only had one card slot (and that was SD not the relatively XQD). It was not even possible to use an EN-EL15 form factor for the battery but rather had to rely on an advanced EN-EL14 design. This did not lead to overall rejection of the camera, the Df proved to be more than worthy despite this limited features. Luckily the Z-Series is using an EN-EL15 (like it was the advantage of V1 as the only member of the Nikon1 line). So i see no issue against buying and using a Z so far. Of course the Df is less energy consuming, currently it is not clear how many shots the Z series can do given the contradictional statements existing.
I'll also add to this from my experience with mirrorless cameras.
Coming from Fuji and Olympus as a background, just to level set.
Specifically talking about the Olympus OMD Em1 Mark II here. The dynamic for the cameras in mirrorless may very well need to be changed from shots per battery to shots and power on time per battery.
What I noticed with battery power is much more about how long the camera is on versus how many shots it takes. The EM1.2 could get pretty close to 1000 shots per charge, if I was continuously shooting with it.
In a blog post I did, I put the Nikon D500 against the EM1.2 at a hockey match. The Nikon did about 10-15% better on battery than the Olympus, given comparable shooting conditions.
Now, if I took a few shots, left the Olympus on and went about my business, came back and took a few more shots and did that...then I would be getting about 200-300 shots per battery.
However, I could get double that or more if I took a few shots, turned the camera off, went about my business, then turned it back on to grab the next series of shots. That is one thing that the DSLR is still very much king on. You can turn it on and leave it on and it used very little battery in that state. Only when you review images or activate the exposure metering or VR does it start to really consume energy.
So, at the end of the day, if switching to a mirrorless camera, shooting discipline changes should most certainly be a consideration to maximize battery life.