Live Rock will seed the sand, not necessary to buy "Live Sand" unless you have another reason to do so. On the background, I like the blue look, personally, however it shows more imperfections/bubbles when you apply it if you don't do it perfectly or if you get a print that's blue based, it's cool like Seaview's "Seascape," looks like endless ocean.
As for cleaning the tank, I'd use vinegar & tap water 50/50. Just let it dry completely before you start setting it up--don't use towels to dry it that have been washed w/ laundry detergent (& fabric softeners)!
On saltwater... Petco pre-mixed is expensive. Shouldn't mix your own w/ tap water due to possibly toxic levels of TDS
such as Copper which once in your tank even if you don't plan to keep inverts now, you might later. Copper hangs out even when the offending water is gone. My LFS
. I just buy it mixed, easier & honestly won't be saving much money buying salt for all the trouble. Up to you though & what's available, you gotta do the math