I would get the tank cleaned out of freshwater inhabitants and then get it filled with RO water. RO because its better for saltwater. dump in salt and let it mix with the powerheads and get it up to the proper level. Leave a few inches from the top so you can add the sand after a little while. Dont use the filter until you have the sand and rock in the tank because the water line will be low, after adding sand and rock raise the water line however much you need to and let the filter do its job. run it with just floss for a few days. you can add carbon if you would like but not needed at this stage. after the tank clears up for a week or two and all the levels are good, temp, salinity, ammonia, nitrite, nitrate, pH, etc, then add a small clean up crew. these guys will kick off the tank and get some bacteria buildup going. very important. after this get a stocking list put together and let us know what your plans are so we can help you with that as well if you need it. use the same thread so we can go from start to finish.
