I absolutely agree with you here. Launching from the moon would be a huge savings in fuel and if you did it right you could then use the Earth as a slingshot to increase speeds substantially.
Yes with deposits of water on the moon you would not have to import a lot of water. The filtering and cleansing of the water can make life more easy on a moon base and farms can be growing food there allowing a much more sustainable base with lots of oxygen that is regenerated by the growing plants.
On second thought, the Moon's water may be widespread and immobile. A new analysis of data from two lunar missions finds evidence that the Moon's water is widely distributed across the surface and is not confined to a particular region or type of terrain. Source 1s.
Ingredients for water could be made on surface of moon, a chemical factory. When a stream of charged particles known as the solar wind careens onto the moon's surface at 450 kilometers per second (Or nearly 1 million miles per hour), they enrich the moon's surface in ingredients that could make water, scientists have found. Source 6k.