Lines are labeled WF8F signifying a weight forward 8 weight floating line. WF9ST would indicate a weight forward nine weight sinking or sink tip line. For flats fishing use a weight forward line. Sinking lines although useful in some situations, seldom justify the expense initially, and can always be obtained later. A weighted fly coupled to a long leader in most instances can accomplish the same effect as a sinking line, but is easier to handle.
Saltwater fish are large and many species are very capable of emptying a skimpy reel.
The weighted end of your fly line is manufactured with a little extra length added to account for losses to the line when replacing leaders. It is to this loop that you will attach new leaders each time they are needed without losing valuable fly line. Knotted leaders or knot-less ones can be purchased from most fly shops. Knot-less leaders are usually better for shallow water fishing because they don't become snagged in rocks or pick up vegetation. Leaders should be attached to your fly line loop to loop.