Petco brand has,never altered my tanks water, I have hard water as well. It didn't cloud my water, either.
I would suggest the black sand as Petco white sand...is really white, so you see any and all detritus on the floor...makes it look dirty faster. Also, because it's so white, it tends to leach out colors...everything looks washed out.
You could mix back and white together if you don't want black only.
How many inches is kind of up to you. Will you need it to anchor plants? Then I would at least 1 inch. If you don't need it to anchor plants, I would keep it under an inch. If your tank isn't planted and you don't have MTS- Malaysian Trumpet Snails- I would stir the sand at least 1/month during cleaning. I have heard it recommended that you stir sand around at every cleaning.