Welcome the AA. Ask questions here before going the the LFS
. The answers you get here are based on first hand knowledge. The people here will help you with buying the products that you need and not the unneeded products that are paying the rent for the store you are shopping in.
" I bought my tank from a pet store chain and the sales person told me to stay away from live sand and rock."
I say stay away from this store if at all possible. If it is the only shop close by then arm yourself with knowledge before going back.
Nice size tank to start with!