You'll find far better quality locks at home than you'll find here. Remember that you need to lock the frame to something immovable, and ideally the wheels to the frame (though that last doesn't really matter if you're just getting a cruiser). If you get a bike that's visibly better than the other bikes around be sure to keep it well locked at all times, as it will be targetted.
The sand and salt together conspire to destroy a bike. Avoid cables if at all possible, use rustless ones if you have to have them, keep the bearings well greased (don't forget the pedals, which get more abuse than the rest of the bike). Keep all bearings properly tight, so as better to resist grit getting in and destroying them. After riding through floods make sure the pedal bearings especially are well lubricated.
If you have a frame made of mild steel, it's a very good idea to keep well greased the interior of the steerer tube, especially where it joins the front forks. I've seen several nasty accidents where that part has rusted through and failed.