Give Deb's site here, discussing WDW at Large. And make sure to check the many links in the left column of that page....
http://allearsnet.com/tp/ridsiz.htm
Congratulations on winning your trip, how cool is that!!!!

And welcome to the DIS,

you'll find lots of great information and people here.
I just recently have stopped by the disABILITIES, having had the need for a
scooter during my recent trip a few weeks ago, bad back and bothersome knees...getting old, LOL. I found all the info I needed right here and had a great time, scooter and all.
As for size, I am big too, tall, 6' 6". And I do find Disney does VERY well in accommodating ALL people, regardless of shape or whatever. You'll love it.
And again, congratulations, what a neat win!!!