I wouldn't recommend to use RO water. Since all minerals are removed, it has 0 buffer. Your PH will crash completely in an instant as soon as there is something acidic. Just stick with tap water with tap water conditioner. If you absolutely must use RO water, then you also must use a special RO water conditioner to re-buffer the water. In this case, the regular tap water conditioner is not needed.
You should keep dosing ammonia until you are sure that you will add fish into the tank within 24 hours. Right before adding the fish, ammonia and nitrite must be 0ppm but it shouldn't be long, or the bacteria will start to starve to death. You also must do large water change to lower the nitrate as much as possible. Ideally it should be less than 20ppm in a stocked aquarium at any given time. Aim for 5ppm or less before you add the fish. You can do several 50% water change. Two of 50% partial water change will equal to a single 75% large water change.
