A couple of tips here, because I see confused people all the time staring blankly at the Southwest kiosks. (If I seem the slightest bit cranky in this post, I've been running late and stuck behind clueless folks wondering what to do. In these situations, I suddenly become the nicest, mostly helpful person you ever met.)
1) If you have logged in from home, your airport procedure is exactly the same as if you haven't logged in from home. You stand in the same lines, use the same kiosks, etc. When you get to the kiosk, you "log-in" the same as everyone else - which is easiest using your reservation number. If you've left your reservation number at home but printed your boarding pass, the reservation number is that 6-digit code printed right there in big digits on the boarding pass.
2) Speaking of which, since you have to go to the kiosks anyway, there is no need to print your boarding pass ahead of time. Which makes it easy to have a friend (or pay service) log you in if you aren't available exactly 24-hours before your flight. But if you are at home when you log in, you might as well print the thing. If nothing else, it's another piece of paper with the reservation number on it.
3) Note that when you log-in at the airport kiosk after you have already logged in, it won't ask you a yes/no question about whether you want to reprint your boarding pass. There is just a button labeled "reprint boarding pass" with the word YES on it. If you want to print a boarding pass, hit that button. If not, you do nothing.
As for the sit together thing, note that on the vast majority of Southwest flights, an A pass guarantees you will sit together. Heck, in general, unless you are the front of the A line and can snag an exit-row seat, there is no advantage to standing in the A line. So A-pass relax people. Wonder around, sit in the chairs, whatever.
The one exception to this rule are flights where a lot of people stay on the plane from the pervious leg of the journey. This can happen on flights from cities that have many flights, into airports that only have a few (the closest thing Southwest has to hubs). Vegas -> Reno is a good example. I would be very surprised if this were common on flights to MCO.