Firstly, I'm all caught up...sorry you weren't filling well, yay for solo time in the parks, and double yay for catching up with your friends!
And WOW, you're getting SO CLOSE to your next trip. How exciting is it that you'll be Bay Lake Towers!!!! 


I'm positively green with envy (in a good way, of course)!!
Next, I've flown AirTran and found their planes to be among the cleanest I've been on. Rather than try to explain the advance seat selecting process, here is what their website says:
Coach
Advance seat assignments are available for purchase at any time with Discount Coach and Sale fares. Prices vary by seat. For customers who purchase Regular Coach fares (Y, B or M fare classes), some seat selections are complimentary.
You may view the seating options and make your selection during the booking process, or you may retrieve your reservation and select your seat assignments at a later time.
Some seats offer special benefits:
Premium coach seats toward the front of the cabin offer priority boarding
Exit row seats offer additional leg room and priority boarding
All customers choosing exit row seating (whether purchased in advance or assigned at check-in) must meet certain requirements to qualify for exit row seating. See details below for exit row requirements.
Priority Boarding Option -- for discount coach and sale fares
Once you have a seat assignment, if you will be boarding with our general zones, you have the option to stow your bags and settle into your seat sooner. Opt into Priority Boarding during check-in and youll be upgraded to boarding zone 2 from general boarding -- Priority Boarding is $10.00 per passenger.
Hope that helps!
I'll be sure to say a prayer for your cousin!