"...I have no wish to be in MK with several thousands other for Thanksgiving - I just hope my family agrees and we don't do this - but if I have to I would pick LTT."
We actually were in WDW for Thanksgiving, and made a PS for Crystal Palace on T-Day. We were a bit nervous about going to MK but decided to brave it (that, and the fact that they take your credit card number, and charge $10 pp if you don't show up

). It WASN'T bad (unlike Christmas and NY). We only waited 10 minutes at CP after checking in before we were seated, which I thought was amazing, considering the crowd waiting on the porch. We had a nice late lunch with the characters, and a nice break from the park. Yes, we used FP, but still the park didn't feel too crowded.
Our first choice was LTT, but we waited too long to make the PS, and nothing was available - but it has been our experience with that restaurant, that even with a PS, the wait times to be seated are LONG. CP was very pleasant, and there was some traditional Thanksgiving food at the buffet - turkey, pumpkin pie, sweet potatoes.
As far as shops at DD being open - I believe it's business as usual even on holidays.
Have fun planning!