I have an old, 10-12 foot white water kayak. This is not the craft that you want in the salt, although it does handle the surf pretty well. The problem with this yak is that it tracks very poorly in the water (smooth bottom, no rudder). I imagine that you will be doing more traveling in your yak than fishing from it. If this is true, then you want a yak that is easy to get around in while in the salt.
The other issue, small cockpit boats really are a pain to get into even in 8 inches of water (say a submerged sandbar on a rising tide). You can use your paddle to keep from flipping over as you wriggle into the boat but it can be a hassle, especially with some surf crashing in on you as you struggle to get in the boat.
Also, get bladders for the inside of the yak. If you ever do flip it over in deep water then they will be a life saver in terms of getting the yak upright and emptied again. Getting back into the boat...you are screwed if you have a very tight cockpit like I do.
If you do need any kayak advice/supplies then you might want to consider Kittery Trading Post if you are in the area. They have a lot of kayaks and kayaking gear there.
Hope that helps.