Congratulations on completing your first 5K!
As far as suggestions...
1. Find a good half marathon training plan and stick to it!
2. I assume you guys have good running shoes/were fitted for shoes before the 5K...if not, invest in a good pair - for running only - and keep an eye on how much you use them. You should get (I think) 300-500 miles out of a pair of shoes before you need to replace them. If the pair you have now is relatively new it should get you through the half marathon, I think.
3. Since you're going from training for a 5K to training for a half, you're going to need to start thinking a bit more about your apparel (maybe invest in some moisture-wicking clothes? Different socks in case you start to get blisters?), hydration and nutrition during your runs. These are all things you want to figure out during training BEFORE race day.
4. Don't forget your camera on race day!
5. When training gets tough, remember the high you're feeling right now after your first race and imagine how your'e going to feel after completing the half with that beautiful medal around your neck! (I haven't gotten to run the W&D yet and have MAJOR medal envy!)
I'd also suggest looking for W&D race reports on this board so that you can get an idea of how the race works at Disney (packet pick-up, getting to corrals, etc.). Search for Holly (Hollybelle)'s W&D trip report from 2011 in the trip report section...it's pretty detailed and should give you a good idea of what to expect.
And above all else, happy running to you and your wife!!