You don't ever need to add salt directly to the tank (I believe that is what you're asking), but you do need to mix new salt water for water changes. So it's not just an investment of 10g worth of salt - you will need to be able to mix new salt water for water changes every week or two (give or take, depending on the stocking level of the tank and which types of corals you want).
Also once you add the live rock and sand (and powerhead, heater, etc) to the tank, you will need to let the rock finish curing. Depending on where you get the rock, it will be at some level of "cured" - sitting and letting the microorganisms on the rock that have died decompose off the rock. If you get it locally and keep it wet the entire time, it will likely be mostly cured. If you get it shipped, regardless of whether it was already cured, it will have some die-off in transit and will need to be re-cured before adding fish / corals. You can do this with either a piece of raw shrimp decomposing in there, or the rock itself often creates enough ammonia for the cycle with just the junk on the rock that dies. Get yourself an ammonia and nitrate test kit (at least), and once the rock has been in there for a few weeks if the ammonia is at zero and the nitrates are slowly rising, you can start adding coral / fish (slowly).