Freshly mixed saltwater is corrozive, so you will want to age your water in food safe container, aerated for a couple of days, or 12 hours minimum before you add it to your tank. You can use a new tank to hold freshly mixed water, but id hold off and let the water age for a day or two before putting in any LS.
You can save yourself some dosh by just buying aragonite sand, and over a period of time letting LR seed your sand bed. Up to you though.
Agreed, LS is a marketing gimmick IMO. Aragonite sand (half the cost of LS) will seed and become live within a month tops so long as live rock is used.