When you say " current " I think you are refering to Powerheads. Yes you will need powerheads, this is a source of filteration and is a mandatory component for any SW system. You usually want atleast twice the amount of water cycled per hour, but you can always do more. For insant if you set up a 90 gallon system you will want to have enough powerheads to cycle about 180 per hour. On my 325 I cycle 7200 gallons per hour. Seems like alot but its just another aspect to keeping the tank healthy! As for your salt question, when you setting up a Saltwater system I suggest you invest in a RO water unit, basically these system connects to a tap, and preforms reverse osmosis to provide the best water quality. You would only need a 25gallon system per day unit which are fairly cheap. And to make things easier purchase a nice rubbermaid container, this way you can keep track of the number of gallons you are changing, you mix the salt right into the water from the RO unit right in the container, put in a powehead allow the water to keep moving, and when your ready to make the change its all set up. Use a salnity monitor to monitor the level salnity in your show aquarium and the container to ensure its the same, and at a safe level.
Let me know if you follow me, I tend to ge a little confusing at times.
Thanks.