Yes, you can book the Magical Express at the same time you book your rooms.
No, you do not need to get your own luggage.
We flew AirTran in Feb. and used ME. When you arrive in Orlando, no one needs to get their own luggage regardless of airline. You will tag your luggage with the ME tags that you will receive in the mail a few weeks before your trip, and your luggage will be brought to your room a couple hours after you arrive. It won't be on the same bus that you take to your hotel, so make sure anything you will need right away is in your carry-on. (Swimsuit, change of clothes, ID, paperwork for hotel reservation, etc.)
Airtran customers used to have to carry their own luggage for the return trip, but this is no longer the case. Airtran is now an official participating airline with ME. Since they weren't participating yet when we went in Feb, I don't know exactly how that works, but I'm sure you'll get that info in your ME packet. I think you have to check in with luggage services at your hotel on departure day, but I'm not sure if your luggage goes on the same bus with you or gets transported separately. We're just looking forward to not having to lug it all ourselves this time!
We were very impressed with ME. We arrived in Orlando around 9:30pm, had no wait in the ME line, had to wait a while on the bus for a few other people to board, but the seats are very comfy and it was a welcome change after leaving a snow storm and sitting on a full plane for over 2 hours, and got to sit back and relax and watch the palm trees go by as we made our way to the hotel. We still get a rental car, but not for airport transportation. It was much more relaxing to leave that work to someone else!
