Well, I have only done one 5k race at WDW, but there were lots of CM's cheering us on, and then towards the finish (where others were allowed in) there were TONS of people there yelling and cheering, totally gave me that extra boost at the end!! And of course all the great WISH'ers there cheering! It was great!!
As for training, i am doing the Marathoning for Mortals Walk/Run plan. Which basically, by race day, i will be doing an alternating schedule of walking 3 min. then running 2 , for the entire race. So, not completely walking but not running the whole time either.. i find it to be a nice mix. I am not a fast walker - so i can't see me walking the entire time at the 16 m/p/m required pace (which would be a 3.7 or 3.8 - forgot which - on the TM) for me, walking at a 3.7 is about my limit.. then i usally run at about a 5.3. So, believe me, as you can tell, i am not super fast.
I did 4.0 miles the other night in just over 59 minutes, and that was doing a walk 3 min. then run 1 min. (So, i am sure doing running 2 min. will help with my timing..).
I would love to finish at the 3 hr. mark, but who knows.. I just am planning on having the "back of the pack crew" to help cheer me on and vice versa, i think the back of the pack is going to be the fun place to be!

I am sure you can do it, we will all help each other thru it!!!