Dean, I've been doing enough night photography that I style myself as a mini-expert on the subject, so I hope I can help.
First, let's define terms. Night is the time after astronomical twilight when the sun is 18 degrees or more below the horizon. When that happens can vary but two hours after sunset or before sunrise should always be night. Outside of those times, you have some light from the sun. It may be scattering in the upper atmosphere and it may be hard to see, but it is there.
With regard to your questions:
1. Hot pixels. They are feature of every camera and are particularly noticeable with night photography. One of the reasons to shoot in RAW for night photography is that raw conversion programs like Adobe Camera Raw will remove most of the hot pixels in the conversion process. The healing brush tool works great for those that remain.
2. Color Cast. It is almost impossible to get away from light from streetlights and other sources. The brown color cast comes from the ambient light especially that produced by sodium vapor lighting, even though you can hardly see it. Light seems to travel forever. Even the smallest amount of ambient light is likely to be greater than the light generated by the stars so you have to deal with that. In my experience, the best way to deal with the ambient light is to set your white balance to incandescent light. It will turn the brown to blue. If you can set a custom white balance in your camera, choose 3200K. Never set your white balance to Auto because your camera will keep adjusting itself depending on the ambient light, whether the light changes because of a passing car, a cloud over the moon or a big truck passing by a streetlight.
Night time photos don't come out in black and white, they come out in color. Remember that color is reflected light. The problem at night is that there is much much less light than during the day time. If you have a long enough exposure, you will see color. If you are shooting stationary objects like a monument, you can set your ISO to 100 to avoid noise, set your aperture wide open and use a long shutter speed. The light meter in your camera is useless in the dark, so try a 5 minute exposure. Increase or decrease the exposure time until you've found the right exposure time for the conditions.
If you are shooting a scene and want to include the sky, you have to decide if you want star trails or not. Generally star trails are a bad thing unless they are long. Anything less than a 60 minute exposure will just look bad, especially if the trails are not what you are aiming for. So, when you want your stars to be spots and not trails, you have to follow the "Rule of 600" It holds that the shutter speed multiplied by the focal length of the lens should not exceed 600. So, with a 20mm lens, your shutter speed should not exceed 30 seconds. To get a decent photo, you will have to use a high ISO setting.
3. ISO. I think I've answered your questions about this in #2. Your camera will likely allow you to shoot as long as 30 seconds by pressing the shutter button. If you need longer than that, I suggest you get a programmable shutter release cable or a wireless one. You set your camera to bulb and program the shutter release to open the shutter for whatever time you need. Then you don't have time variability.
Since you have an interest in night photography, consider this: You can make long star trails by making lots of exposures and stacking them using stacking software that you can get free or at low cost. Not only can you get some nice star trail photos, you can use video software to create time lapse movies. I made a time lapse movie of the night sky earlier this month. I'll post it to YouTube later and post a link to it. It is 160 images made over about 90 minutes.
Also, go to my website to see some of my night photos. I have a gallery called "After Dark". I also have some in the "New" portfolio. I often include shutter speed in my comments about them. Here's my web address: http://www.goldimagesphoto.com