Hi and welcome to the DIS!
As far as when to book your flight............it's anyone's guess if it is better to do so now or later. My feeling is if you see a fare that you like grab it now. With fuel prices going up and up airlines have started raising fares to cover their extra fuel cost. Of course, you might miss a special fare deal later on if one comes out. Most airlines will charge a fee (like $50.00) to change tickets, but some (I believe SW) do not. I still think if you like a fare go for it. Better to be safe now rather than sorry later.