The spray skirt is designed to keep water out of the boat. It is one of the things that makes a sea kayak seaworthy. It can be popped off very easily by pulling on the grab loop. Once you have done this, and see how easy it is, all your worries about getting trapped will disappear. The greater concern for more experienced boaters is keeping the spray skirt on in surf and rough water.
Sea kayaks are extremely efficient craft.
A strong paddler can cruise at 4 knots and sprint up to 5 or 6 knots, depending on the kayak design. How far you paddle depends on your strength, endurance, sea conditions, and weather. In easy conditions, most paddlers can cover 10 miles in 3 or 4 hours of steady paddling. Most kayaks are far more stable than you might expect. The exceptions are specialized racing kayaks and surf skis, which are designed mainly for flat water racing.