First off, it's Disney. Plan on relaxing and having fun.
To answer a few of your questions:
- The 5K is untimed therefore there are no concerns about pacing. Just keep moving forward and you'll be fine. The worst thing that might happen is that they will close the character lines.
- The character stops are quick in and outs - jump in, get your picture and move on. They are very different than in the park.
- You will be running with about 10,000+ of your closest friends. You will not be "alone." This group will probably do a meet-up in the morning so if you hang around long enough and get to know people here, you could get a chance to meet them in person.
- Yes, there is a place for family to watch you at the end. However, they will probably have to get up with you to come to the start.
- The races start at 5 a.m. I usually try to get there about 2 hours before race time (maybe a little less for the 5K). Most people make the early wake-up to be a lot bigger deal than it actually is.