We have been 3 times, well, once we went on the cruise Christmas day.
Last year we went to MGM. I figured the MK was going to be wayyy too busy. We had dinner at Prime Time and had to wait 2 hours past our PS's. I think a late lunch at a nice restaurant and then snacks or a meal at the resort might be better later at night. The parks were packed but lots of fun as everyone is in the spirit.
We went to the processional the 23rd and again the day after Christmas. The first one was with the package, the second by standing in line. I loved it. We had just not bothered on past trips and I am sorry for that. I might suggest you have an early dinner with the package and do the early processional after. I think you would avoid the crowds that way and then still have lots of time to enjoy Epcot afterward.
We love the holidays at WDW. What ever you do, relax. Know you won't get a lot of rides and events in this trip so just go to enjoy the holidays, the wonderful decorations and to have family time together.
By the way, the first holiday it was in the 80's every day. The second was in the 60-70's and last year we wore our winter coats and gloves and froze. It was in the 50's and windy with the lows in the 40's so...it is impossible to know what to prepare for. We only had rain in Christmas Eve. Luckily that was a non park day for us. We had lunch at WL, spent 2 hours in the water sprites for part of the kid's present and then had dinner at Spoodles. We also went to a movie at DTD. It was a busy day and a wet one.