We are last looking last minute at a possible couple days at the parks around Dec 20. We made our first disney trip a few year ago and it was wonderful using touring plans…we waited maybe 10 minutes 2 times the whole week. I can NEVER do Disney with long lines now, NEVER. It is my understanding there are currently no fast passes? When will the new Geenie(?) system start? I spent so much time planning our first trip and learning the ropes…do I need to spend tons of time learning this new system now too? Even with the new system, will we expect long lines around Dec 20th? Help, totally confused 
The 20th won’t be as congested as the following week. Correct, no more “fastpasses,” however with early every for onsite guests you’ll be able to get a nice head start.
Use your TP and “optimize.” My guess is, Disney avenue & Genie+ will have started, so that’s another option.