Start cycling your tank, find a good substrate, add salt obviously, start your heater, filter, etc. add LR asap, you can get large pieces but you pay by weight so look for porous pieces that feel light. Look for growth on them, especially purple corline algae. Don't pay more than seven a pound and start with about twenty pounds, then add more as you like.
If you plan on fish only then you can get away with less liverock LR if you have good filtration, an established livesand substrate which you can seed with LR and bacterial addatives as I did. You can buy the stuff online for ten bucks and substrate at twenty bucks a bag, you'll need three bags. Add a raw shrimp to start your nitrogen cycle, take it out if it gets nasty. That will get bacteria going. Bring water to get tested after a few weeks. Add simple cheap fish to start.