If you haven't done
MVMCP before, I would recommend trying it once. It's just a little extra magical.
The week before you leave, look at the weather forecast and adjust your packing based on that. As others have mentioned, the weather can be all over the place.
It will be busy. Set your expectations that you won't get everything done that you might normally do. Plan for some time to go to the different resorts and check out the Christmas decorations. Look at doing other non-park things on this trip. Mini Golf, Fort Wilderness Campground activities, etc...
You might want to explore doing a split stay so that you are staying close to the parks that you will be going to. For example, book part of your stay in one of the EPCOT area resorts and then go to EPCOT and HS on those days. Then move to the MK area and do MK on those days. We will frequently do AK on our move day since we have to take a bus there regardless of where we stay. In addition to the parks being busy, the roads will also be busy during that time, so getting places will probably take longer too. This is the approach we usually take during non-busy times, but for sure during busy times.
In addition to it being busier, it will also be more expensive. So, you might need to budget a little more for food and stuff.
Given the number of people in your party, I would lean more towards taking Mears Connect to and from your hotel. That way you can all stay together and it will probably be more economical. If staying together for the that part of the trip isn't an issue, I would go for Uber/Lyft.
Have a great trip and happy planning!