This greatly depends on what kind of filtration you are planning to use or are using
What kind of tank are you keeping; reef or FO
I don't see LR
in the setup...are you planning on having some?
10 more lbs or so of the Southdown sand and don't get too many critters that sift the sand..at least for 6 months or so...Let the sand bed become active with little buggers. You want the sand to be a breeding ground for pods
and worms and such...This will be your best de-nitrification in your tank...If you get a lot of critters that sift, they will wipe out any colonies and therefore reduce the amount of DN your sand bed will produce..