I'm quite ok with the number of light trails.
Colour balanc elooks fine, those high pressure sodium lamps are pinky yellow. However, colour baalance on a shot like this can be very subjective. If you shoot in RAW you have much more flexibility in changing it in post processing without affecting image qualithy, though you may end up with several versions all of which you like!
if possible shooting earler when there is some deep blue colour in the sky would give some separation between sky and land. I do think the black sky here does simplify the range of colours in the image and is ok as you've plenty of street lamps in the top part of the image.
The starbursts are just a function of using a small aperture.
You don't need f/20 as it's not giving you the best lens performance though i do see that it helps give you th elong exposure. Your camera does go to ISO 100, so setting that you could use f/13 for better performance and get the same shutter duration, and still no worries about depth of field either.