Try about ISO 200 @ f/8 for 30 seconds and work from there. That's three stops slower ISO and 4 stops (and change) slower aperture, so that is seven stops slower than what you used. Since some of your highlights appear to be slightly blown, lengthen the shutter speed by only six stops from 1/2 to 30 seconds for your starting point. If you haven't already, learn to use the histogram to judge exposure, rather than how bright it looks on your LCD screen.
Because the two towers of the bridge are at rather dissimilar distances, you need to use a narrower aperture to increase depth of field. This will allow both to be in better focus.
To reduce the noise use a lower ISO and a longer shutter speed. This will necessitate a very stable tripod and a way of remotely triggering the shutter. A wired cable release usually works better for longer exposures than an infrared remote that often limits use of available camera features. The wired remote usually allows you to set the camera the same and use all of the features available using the built-in shutter button. Try to shoot when the wind is not very string, as that can cause camera movement on even the best tripods.
The main reason the color of the sky is off is due to the type of lights illuminating the bridge. They appear to be very narrow spectrum sodium vapor lights. Trying to correct for them so the bridge is the right color will make the sky very blue, rather than black. Using a color temperature/white balance that is correct for the sky will make the bridge very orange or even yellow. Leaving the shadows/sky darker will help. You can do this with light curves in post processing, but creating separate layers for each area and correcting each for exposure and white balance independently should yield better results for an advanced editor.
Here's a scene I shot a couple of years ago: Due to many of the lights cycling on and off every few seconds as well as the water flowing very rapidly out of the discharge chutes under the power house I used very high ISO and wide aperture in order to allow shorter shutter speeds. It was also very windy that evening. All of the shots I tried at lower ISO, narrower apertures, and very long shutter speeds fell victim to camera movement caused by the wind. The first image below is an HDR image that combined two shots exposed 3 stops apart. ISO 5000, f/2.8, for 1/30 and 1/4 seconds respectively. Global adjustments only in processing. I raised exposure 0.17 stops in post, as well as reduced contrast, pulled down the highlights and raised the shadows rather aggressively. Notice the more modern lights over the lock on the other side of the river than show up a more neutral white color. I probably should have backed off the color saturation a bit more in the HDR module as well. At least in my case, I don't think HDR really helped much in this scenario.
The same scene from a single long exposure. ISO 160, f/8, 8 seconds. Notice the trees in the lower foreground that were being tossed to and fro by the breeze, as well as the blurry water discharging from under the power house. I adjusted the color temperature cooler at 2700ºK and also used less color saturation. Notice the brighter lights over the lock across the river have a very blue tint to them, but the orange sodium lights are a lighter shade of yellow rather than a deep orange. I raised exposure 0.17 stops in post, as well as reduced contrast, pulled down the highlights and raised the shadows rather aggressively. The increased depth of field by using f/8, rather than f/2.8, makes the entire scene (other than the wind tossed trees) look better.
As far as HDR versus stacking images all exposed at the same E.V.: HDR processing can lead to increasing the perceived noise along with the increased edge detail. Stacking tends to neutralize shot noise, which is more influential in long exposures. It doesn't affect read noise, more the concern in shorter exposures, much either way.
