cobbler, that sounds like a good plan! Although, you've got to have serious guts to do the Goofy. I'm always exhausted the day after race day, can't imagine doing a marathon after a half, or vice versa.
A lot of people who do the Goofy usually go at a slower pace for the half so that they are not exhausted the next day. If you go all out for the half then yes, you will be exhausted. Amy, when you go Goofy, I suspect we'll have to put you on a leash for the half to hold you back some.

cobbler - I think your plan to postpone the marathon may be wise although like someone mentioned, you might change your mind after the W&D half. Crazy things get in our heads after these Disney races. After I did my first half (at WDW), I swore I'd scratch this off my bucket list. I had a horrible experience. However, three days later, I signed up for the marathon for 2008. It happens.

As for training, maybe some others can share their experiences. For me, I always had a half-marathon or two or three planned down the road so that kept me in the training mode until the official training started for the marathon/Goofy.