Beca, I raced the FL 70.3(half Ironman distance) race in May. I'm not at this time planning to do the International distance in September as my main race for this season is Ironman Wisconsin on Sept 10th. The swim for both events is in Bay Lake starting at Fort Wilderness. The water is warm enough to not be wetsuit legal. It's very dark w/ tannins as is typical of southern lakes. The area on Disney property and immediately surrounding it is pancake flat- very fast for cycling. We went further out into the next county which was hillier on our bike since it was a 56 mile loop but it was still very fast in my opinion. The run was again pancake flat but w/ very little shade and 93 degrees for 13.1 miles. Our run was 3 loops around Fort Wilderness and Wilderness Lodge whereas my understanding of the Sept course is that you run to Epcot. The biggest hills on Disney property are on/off ramps so any course should be fairly flat.
I live in the northeast so I flew to the FL 70.3 and earlier in the year St Anthony's Triathlon in St Petersburg, FL. I will also fly to Wisconsin(Madison) in September so I bought a nice bike box off Ebay this winter. Many bike shops rent them though and that can be a more economical option if you aren't going to be flying fairly frequently w/ a bike. You can either fly w/ it or ship it to a local bike shop(Orange Cycles in Orlando I think) and pay them to re-assemble it for you. Another option for some races is a business called tribiketransport but I don't know if they are doing the international distance at Disney(they did the 70.3). It's a neat concept- they have special trucks that the bikes get loaded into fully assembled at a local(relatively- they only work w/ certain shops and not close to me) shop and then unloaded at the race site and then the return process to get it home.
Feel free to post triathlon questions on the main thread too. There are at least 5 others that I know of besides myself that have either done triathlons or are in training to. I ran the full at WDW last January, the Minnie in May and am going Goofy this January but I'm primarily a triathlete that is trying to work on a relatively weak run for the level I compete at. Wisconsin will be my third Ironman plus I'm doing a total of at least 4 and likely 5 half Ironman distance races this year.