It's not that live sand isn't needed, it's just that the stuff you buy on the shelves claiming to be Live really isn't because - well it's been sitting on a shelf. You can use the same type of sand, just buy it dry and it'll get seeded and become live on it's own. Personally I use the dry Aragamax sugar oolite. It's a whole lot cheaper than "live" sand from the shelf, and works the same in the long run.
You can buy non-live rock (aka base rock) and seed it just as you said. A better way would be to take 1 rock from your existing system and place it into the new, rather than going the other route. You need several weeks to really seed a rock, so that'll slow down your progress if you do it as you mentioned.
If you do buy base rock, you'll want to cure it first IF you're going to put it in your established tank (unless you're just going to do a small piece, you'll probably be okay without curing it). If it's going straight into the new, uncycled tank, just rinse it off really well before putting it in there.
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