You will LOVE this time of year. We have been twice and both times our dates fell just like yours - we were leaving as the crowds were arriving. I remember one visit, we were leaving on Dec 21 (it was the Saturday before Christmas that year). We were on the monorail and it looked like someone had opened the flood gates of people pouring into MK and all the resorts! The place had been seemingly empty until then.
The place will be as close to empty as you will ever see it. Still avoid MK on Saturdays (and maybe Mondays), but besides that you don't need to worry about it at all!
As for rides, I've never seen anything closed during this time. In fact, there seemed to be a lot of extra CMs during this time. We were told on one trip by a CM that Disney hired lots of extra temps for the Christmas rush. Those people are on the job by early December learning their jobs and getting ready for the rush. I would think that same logic would spill over into ride rehabs.
We have NEVER (yes, I literally mean never) waited in a line anywhere in WDW in early-mid December during regular park hours. (I am sure you won't believe that, but it is true. My kids don't even comprehend waiting in lines at Disney World.) One word of caution: Mickey's Very Merry Christmas Party. It is a wonderful thing, wouldn't miss it, but be careful what day you go (if you go). Tuesdays tend to be better than Saturdays. We did encounter crowds on a Saturday
MVMCP once.
We walked into every restaurant we wanted without ressies. (BUT! You will still need Cindy's castle ressies if you want to do that.)
It is a GREAT time to visit! Not only are the decorations beautiful, the lack of crowds allows you to visit things at a much more leisurely pace. AND and many, many CMs allow for much more interaction and lots of extra things: once a Living Statue at Italy played with my kids, my hubby got called up to do the slap dance at Germany, my son was called on stage at Hoop Dee Doo, my daughter was called up to do the belly dance in Morrocco, a talking trash can literally chased us down in Tomorrowland, we had several times where we were the only people visiting a character, the list goes on and on. These things are more likely to happen then because there are less guests to chose from.
Have a great time!!