I think that Friday the 12th will be pretty busy because of the novelty of the holiday decorations going up. Truth be told, most of the stationary decorations will already be up in the days/week leading up to 11/12, but the holiday entertainment begins on 11/12, such as Santa, the carolers, the nighttime Winter Castle light 'show' up Main Street, the snow, IASW Holiday, the Round-Up, etc. It will be busier than a Friday when there are no holiday decorations, in other words.
But, my thinking is that it will likely get busier in the second half of 11/12 and for that weekend because the Deluxe AP holders, the Premium AP holders and the Premier AP holders (who live nearby) can all stop by DLR after they get off work to take in the sights. I know this happened last year - quite a few locals who have APs higher than the SoCal kind went to the park on opening day of the festivities and they said it was rather crowded.
As for 11/11, It has been suggested (I think it was on our Christmas thread?) that it's likely that most of the people who have taken a vacation to be at DLR over Veterans Day will probably also stay through 11/12 or 11/13 (just like your friend, Susie63) to get a little taste of the holiday entertainment. So that would add to the crowds.
I've never heard of the days surrounding the holiday start date being crazy, crazy, New Year's Eve-ish crowds. So it won't be up to that level, which may be reassuring. But I would expect there to be quite a few people.
Also, depending on World of Color and what happens with that during Fall and Winter, that might cause an increase in attendance. WoC was not a factor that we had to contend with last year, so WoC + the (already busy) holiday season is a big question mark at this point.