I would recommend adding a powerhead as well and use a refractometer for measuring salinity. Do you want it to be a reef? If so then think about using ro
water, no tap water for a reef tank
you will also need powerful lighting for that.
I would suggest around 20 - 30 pounds of live rock (rock first, then sand) to start the cycle. You can use pure ammonia or a raw shrimp form the grocery store for that. Check out the articles on here on how to set up a salt tank, there is great info on how to cycle a tank properly...