First, I agree with Brent: this is a fantastic image that even a pro would be proud of.

Regarding finding focus, I did a bit of research and tried about everything before finally finding my technique (I shoot with a Samyang 24 and also a 14, which is even more difficult to focus.) I use live view because I shoot with Sony, so that's a given. I also use focus magnification and I concentrate on a bright star or, if I have a bright distant light such as in your image, I might concentrate on one of the very-distant lights (if the distant lights are in focus, so will be the stars). If necessary, I'll temporarily bump up my ISO really high to make the pinpoints brighter in my viewfinder. Then, I slowly rock the focus ring back and forth and narrow in on the pinpoint until it is the smallest possible point -- because when the pinpoint is smallest, it is sharpest. I get better results than even using focus peaking.