Definitely not crazy. I started training in July 2011 for the Halloween 5k, then immediately signed up for the Princess and started training with the Princess training program which started the same week with a 3 mile run. Finished the 2012 Princess as my first half, and have done 5 more since!
My suggesion is to sign up for a 5k around September/October. The Galloway 5k training plan is 15 weeks and starts at just 10-15 minutes. If you live near Disney, I suggest you sign up for the 5k attached to ToT, follow the Galloway 5k plan, and then switch over to the Princess plan, which should start with 3 miles the same weekend. If you do that, there is no way you won't finish the Princess!
Edit: I was also 40 pounds overweight and seriously had negative running experience. I was always the last kid to cross the finish line in the mile in high school. I had a Disney 5k on my bucket list, and no one thought I would even do that! I am now 40 pounds lighter, running three times a week, doing strength training two to three times a week, and basically a healthy person. I highly suggest the Galloway plan to anyone!