For sand, you can buy live sand or normal sand from Petmart or 328 cheap. If live sand, you don't need to wash. Can immediately pour into the tank but if normal sand, you need to wash a few times before adding into the tank. Also good to add bacteria when cycling tank to aid in break-in process.
For live rocks, advisable to get huge live rocks which will look good in the aquascaping. Most reefers who decom only have medium pcs. You can go coral farm for good rocks and try LCK as sometimes they have nice ones. I will likely be going there with a friend on Fri as I'm helping him with re-scaping his tank so if you want to join us, you are welcome to. Pm me.