Welcome to the club.
Your LR and sand will be just fine without your sump. Proper salinity, heat and circulation will keep your LR alive indefinitely. Skimming just helps remove the junk from your water. If your LR is cured and you are not adding any fish or corals the balance should be just fine. If you are worried, test your levels and do several water changes, but it will be fine.
For your sump, a poly filter or sock will help trap detris from entering your sump and help polish your water, but you will have to change and clean it frequently. You don't need bio balls or sponges in your sump. Your sand, live rock and skimmer will be your main filtering mechanism. Water changes will also help with this.
Goodluck.
Brandon