Get a dechlorinator such as Prime as mentioned above. Using tap water you run the risk of having chloramine in the water as well as chlorine. While chlorine will evaporate out of the tank in 12-24hours, chloramine does not evaporate and will stay in the water until it can react with something (your fish). Prime is cheap, lasts almost forever, and a good guarantee that your water is good for the fish.
If this is the first tank setup, I like your idea. When I first bought my tank I cleaned it with tap water and a paper towel to get any debris off, and then filled it with tap water. I hooked up all my equipment (filter, heater, decorations and substrate) and let it cycle for a day or two. This way I was sure that if any unwanted bacteria/fungus/algae was present in the tank, it was now dead. Obviously don't hook up the filter if your using seeded material until after you've treated the water!
HTH,
justin