1. Train. Train and Train and TRAIN! Start now, you have plenty of time to ease in and then get down to business towards the end of this year. I started in July of last year, as a complete non-runner, someone who exercised once a week. I did great.
2. Don't let how complicated it all seems scare you. Stick to these boards, Disney maps things out so well, you'll be fine. I was very intimidated by the process but it all ran very smoothly when I arrived.
3. Give yourself lots of time down there. Time for the Expo(it can get very busy), time to get to the race, etc.
Yes, some ladies do it all. The 5k and the half, or the kids races and the half. This year I just did the half, no other events. Next year it will be a family trip and we'll do more of the family races with our kids. The 5k is early Saturday morning and the kids races are after that.
The Expo itself runs Friday and Saturday. This is where you bring in your signed waivers(which you get a few weeks before the race), where you pick up your bib and race goodies(t-shirt and stuff). There are also lots of vendors so you can do shopping. I recommend going very early if you can, it gets busy fast, and there are commemorative items that Disney sells(like shirts that say "I Did It!" with the race info) that sell out pretty quickly. I went when they opened on the first day, didn't fight lines and got the items I wanted, like the t-shirt.
Prepare for all kinds of weather. I've heard in the past it's been chilly and/or rainy. This year was very much not. It was very warm(70 degrees when we left at 3am) and extremely humid, humidity in the mid to upper 90s. It was rough on a lot of people, esp people coming from the cold north. Make sure you know how to fuel your body and properly hydrate. Training now helps with more than just getting ready to run, it helps you practice how to treat your body in different conditions, since you'll run in the spring, the heat of summer, the temps in fall and winter. Longer training runs will also help you tinker with the right ways to fuel your body. Everyone is different when it comes to that.
Disney has add ons all weekend, from breakfast after the 5k, a pasta party the evening before the race, race retreat(a special tent you pay to get in to before and after the race with extra amenities), ChEar packages if you have family coming to watch.
Lastly, my biggest piece of advice, besides training, is to relax and have fun! This year was my first year. I can't tell you how much I stressed in the months leading up to it. The idea of getting swept and not finishing, the idea of not being ready, just the weekend in general, because it was unknown to me. Turns out I had nothing to worry about and I probably just annoyed my travel buddy with my constant stream of questions and fretting lol. I trained plenty and was physically ready for the race. There was little pressure, Disney puts on a great race, I had a lot of fun, and it's so fulfilling.