Maybe cycle the sand in a seperate tank, but most of us don't have that... So if it was me, I would probably add a little bit at a time. Lets say, quarter inch or so, leave it for 1-2 weeks, then do the same, until you have the depth you want.
I would also really rinse it, prior to adding. But you knew that already
Good Luck!
P.S. I too have jumped on the wrasse bandwagon, great fish... Thicklip banner wrasse, potters, black leapord, bluish colored leopard, 6 line (I love the quirkiness of six lines).