Like you, after spending quite a while reading the posts on here I decided to start posting myself, so welcome.
I went this past new years with my girlfriend. It was my first trip down there durring this time of year. The experience is pretty different then durring the summer months. I will do my best to answer your post in an organized mannor, but I doubt that will happen.
Wait times can be very long. The wait times for rides like Toy Story Midway Mania, Sorin, Mission: Space were between 2 and 3 and a half hours. Rides like The Many Adventures of Winnie the Pooh or Peter Pan's Flight were 90 mins.
Take advantage of the EMH! Especially the PM ones. The park clears out pretty quickly, people will usually just stay for another ride or 2, but the lines are much shorter. If you plan in staying in the park for the PM EMH, don't rush to get to the park durring the day since you can stay until much later. Also, fast past when possible.
MK and EPCOT will close, especially on the 30th and 31st, due to capacity mid-day, but will re-open by the beginning of dinner time, I was in EPCOT by 3 right after it re-opened on New Year's Eve so I don't know if they shut down after that. If you are going to eat in either of those parks, plan accordingly.
EPCOT is the place to be on New Year's Eve if you get the chance. It's packed but it seemed like every country in the WS had its own music and party going on. It was a lot of fun. You can still see the MK New Year's Eve fireworks on Dec. 30th.
Take notice of each parks x-mas trees. They are decorated in thier own unique way.
We stayed at POR, and even though it was booked, the layout of the resort made it seem like no one was there. We had breakfast pretty early and came back pretty late (it's nice to be young and full of energy).
Get your ADR's as soon as you can because everything will fill up, TS for both lunch and dinner fills up in most places, so don't expect to be able to just walk into a TS restauraunt and get a table.
But the 3 most important things are, 1) remember you are there durring the busiest most chaotic time of the year, just be patient and stay calm even when you just want to scream on the top of your lungs, 2) people watching is a fantastic way to pass the time and the people watching options are endless, and 3) have fun!