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It would make a great first marathon! Easy course (relatively speaking...it's still 26.2 miles!), great support as far as the aid stations, mile markers, etc. Pre-race checkin/packet pickup is very well organized.
First...if you haven't signed up, I looked on the race page and there are only about 350 spots left. It is a huge race...you will never be alone on that running course! And lots of people use it for their first marathon...lots of people do it through the Team in Training program for the Leukemia and Lymphoma society, so you will see lots of purple tops out there, and they bring a good crowd of supporters.
As far as crowd support; the main viewing areas are by the start (though I would recommend letting your DH and kids sleep and catching you running later...I ran 4:44 last year, so my friend had plenty of time to find me), at the TTC before you go to MK, by the monorail resorts, Main Street of MK, as well as the other parks. Some folks drove to other points along the way to watch, but that would mean having a car out there, and with the limited roads, that seems like more trouble than it's worth. If your family watches from Main Street, I think they can get in without a park ticket, but then will have to leave.
The course is great...almost all flat except for a couple of overpasses/underpasses. The parts of the parks that you run through will be coned off, so you're not dodging park visitors (of course, you have Epcot all to yourself at 6 am!). The background music that plays in the parks makes it feel like you're hardly putting out any effort. The roads between the parks can get a little boring, but then again, there are so many runners, you can just people watch! There is occasional entertainment on the non-park sections. You'll see lots of characters along the way...I think I counted 36 different characters last year. Lots of folks bring disposable cameras and take pics along the way...I didn't this year, as I was going for time. Water stops are every mile.
My friend that watched me had a park hopper, though she just went from TTC to the halfway point (parking lot by poly/TTC) to Epcot. We went back to Epcot for the traditional post-race margarita after I showered. Once you know where you're staying, if I could be of any help to map out spectator points, let me know...I'm a good race spectator as well. I do triathlon and have watched some Ironman events...spectating takes special logistics, but is super fun!
The 3 am wakeup call is the hardest part of this race.

The race starts at 6 am...I'm sure it's a logistic thing, to get us all going and get the race done, as we take up lots of road space. They want everyone in the staging area (Epcot parking lot) by 5 am, and start moving towards the race start (behind the World Showcase on a road) at 5 am, for a nice wait in the start corrals (based on estimated time...). The last 2 years have been nice and cold at race start...so lots of people had either extra sweatshirts to toss once they warmed up, or garbage bags to keep the wind off. The first mile or two of the race course on the sides looks like a Goodwill truck exploded! It isn't so lovely to get up so early, but moving 20000+ runners from one place to another takes time.