1. It is not a good idea to wash your filter media with regular tap water. The tap water can kill the beneficial bacteria that is built up in the filter. Use distilled water to clean out your filter and its components.
2. When you purchase your aquarium and the equipment for your setup, do not purchase the fish at the same time. You are going to need plenty of time to cycle the water in the aquarium to make it hospitable for the fish in your aquarium.
3. You should always purchase the correct lighting setup for your aquarium. Doing this will make the habitat much better for the fish and plants in your aquarium.