This is the way I would do it since the tank is empty and you should never mix salt this way once you have sand, live rock, inverts etc.... Fill tank with RO water and use general guide lines on bag / bucket for mixing salt. Turn on heater (80 degrees), powerheads, and filter and let run for 24 hours. After the 24 hours has past test your salinty and specific gravity and slowly add salt till you reach level you want. You want to shoot for between 1.023 for fish only and 1.026 for reef. After your temp has reached 80 and your salt level is stabilized where you want it for 24 hours you can go out and buy some sand (1lbs per gallon). You can save alot of money by buying 1/2 the amount of sand as dry argonite and the other 1/2 as live sand. This is also a way you can save alot of $$$ for the rock. Buy 1/2 the rock as base rock and the other 1/2 as cured liver rock(1 to 2 lbs per gallon).
Use a raw shrimp to start the cycle of your tank and never use a fish. Make sure you have a test kit to test the nitrate, nitrate, ammonia, and ph of your water. You should test all four of these everyday while your tank is cycling (research nitrogen cycle).
Welcome to the boards!