First SW in my opinion is great to fly. If you purchase a ticket it just like any other airline there is a slim chance that you could be bumped. I"ve never had it happen on any of the flights I have ever flown on though.
In my opinon it he only difference is the full rate fare you can get all your money back no problem. All the other fares you can cancel your ressie and get a credit without any problem. The credit must be used within one year of ressie date.
I ususally pick the cheapest fare "internet rate" then wait for a DING and get an even better price.
I prefer to book each leg individually as that makes it easier to make changes to the ressies if a price decrease occurs.
But the seating is always first come first serve. They have what they refer to as "cattle call" seating. You are assigned an A, B or C borading pass. YOu can register online within 24hrs of your flight to get your boarding pass. When you get to the airport there will be 3 lines and you enter which ever boarding pass you are...except if you have an infant, toddler or disablity you can then pre-board.