There is indeed no technical difference mentioned in the description of the generation 1 and 2. I chose the generation 2 card because the price difference between the two is really minimal considering the cost of the case, and the employee at the Digitec shop in Geneva confirmed that it was slightly more powerful than the generation 1.

The XQD 2.0 have an interface that supports PCIe V2 and USB 3.0. The XQD 2.0 G series have an interface that supports PCIe V3 and USB 3.1. They are therefore faster.

Sony is the manufacturer of such cards. Nikon only buys them (presumably from Sony, like the sensors) and sticks its label on them. You certainly can't go wrong with Sony memory cards. SanDisk is owned by Western Digital. Very renowned. You can definitely buy them.

There are several readers available, one is the Sony MRW-E90 XQD SD Card Reader.

According to Sony, this card is not affected by X-rays or low temperatures.