Vacuum out the gravel really well one day, and again the next. The % water change isn't important, just clean the gravel.
Sand is much more natural. Effectively all of the fish we keep in the hobby are from waters that have sand (or finer) as a substrate, not gravel.
Sand is also cleaner. It keeps debris on top. If you have enough flow the debris will keep moving until the filter grabs it. If you don't have enough flow you will get a few piles of debris and all you have to do is hold the gravel vacuum over those piles and they will lift right up and get sucked out. Although you can get some very fine debris in the sand over time, it is nothing compared to gravel. Some people stir it occasionally or before a water change, but I don't do this. I am sure I would stir some stuff up if I did, but it is not bad enough to worry about.
Estes' Ultra Reef doesn't even need to be rinsed, just pour it in the tank. It will stick to the surface and bubbles at first, but it is pretty easy to get them all to settle. This is all the work you will ever have to do for this sand.
Dark substrates and backgrounds cause the fish to increase the actual amount of pigmentation in their skin. They will be physiologically more colorful. The darker background and substrate will also show off these colors better. The mixed black and white looks good, is dark, but still hides any debris that may settle on the bottom.