I've flown southwest a number of times and had great luck.
You can book your flight down now , and book the return at a later date, as all their flights are booked one way at a time anyway.If you book before a ding comes out, you can get credit for future fare only, most internet tickets are not refundable,you must also do this via the website, if you call they will charge you extra.If you do call, they will tell you how to do it, and one lady last year was nice enough to direct me to the website, telling me it would be the cheaper way to go.
Be aware that there is whats called open seating on Southwest, and that you must check in early(like 24 hours early) in order to get the seats you want.There are no reserved seats, you just sit where thetre is an open one as you enter the plane.The earlier you check in the better seat you can get.They give you a letter at check in..A, B, or C A's board first, then B's then C's A's get good seats, B's ger ok seats, and C's get wedged whever there is room left.If you have a big group and you all need to sit together, you better check in online as soon as you can, and get in line at the gate early.If you do all this, I've found southwest to be a great affordable way to get to Orlando