All of the info about getting started, finding information, staying motivated, etc. is definitely on target. Whether you ever run a Disney race or not I think there are tons of bonuses to improving your health and losing weight.
However, I skimmed all the responses and didn't see any mention that RunDisney 5K and 10K sell out fast. Although I've never run during Princess Weekend I'm pretty sure Princess sells out the fastest of all weekends; for comparison, the 5K and 10K during Marathon Weekend have sold out within the first hour of registration for the last few years. I'm not sure how the new registration system will work, but depending on what mode of registration you are looking to use (Normal, AP/DVC,
Travel Agent) you will likely have to be on top of registration dates, times and methods. If running those two races during Princess Weekend are going to be a big motivation then you'll need to make sure you're ready for registration so that you don't have the disappointment of missing out on your desired races potentially dragging down your plan.