By adding salt to the water you are increasing the number of dissolved particles in the water (this is quantitated as the molality of the solution). This decreases the freezing point of water and therefore the temperature of the ice/water mixture because it will always equilibrate at the freezing point of water as long as there is both ice and water present in the mixture. This is known as "freezing point depression".

You have a misconception in your understanding of the expansion of space. All space is expanding but at different rates according to how far away from us the observed object is. So for instance, the space between us and the sun is expanding, but at a much slower rate than the rate between us and distant objects. Distant objects have more space between us and them, and therefore more rapid expansion. The only limit to our observations is the resolution of our telescopes. Even galaxies that formed just after the Big Bang are observable, but because they are so far away their light has been red shifted into the infrared, and therefore we need an infrared telescope to observe them (hence the Spitzer telescope, which will make observations right up to the Big Bang event).