Most North Koreans don't have laptops, so that would not make a lot of sense. TOR was originally sponsored by the U.S. Naval Research Laboratory. The U.S. State Department, the Broadcasting Board of Governors, and the National Science Foundation are major contributors according to Wikipedia. Privacy is very important for the military, so I would not be to surprised if it was developed for that reason. Nevertheless, even with TOR the mass surveillance program makes the US more vulnerable.
It's isolated but at the same time it's open. People can visit as tourist. They can be watched 24/7 trough satellite images and drones.
In addition, there is an underground tunnel network to South Korea, which could also be used.
Very true, the only reason NK still exists is because of China. If China would not be their ally, there would be one Korea now.
They should become more like China, the life for NK citizens would be better.