You will probably have a hard time finding an open restaurant on Christmas Day, and maybe on Christmas Eve after early afternoon. Perhaps restaurants in international hotels will be open for meals. Whatever you find, make reservations well in advance. Many sights will be closed.
I don't think you need a private guide for Versailles. Please look at the website for Versailles for options about tours there. Many people do not buy the museum pass because you can no longer make multiple entries to a museum with the pass due to timed entry requirements. Just reserve your time (as early in the day as possible for the Louvre orOrsay) and order tickets online. Take a look at what is covered with the museum pass and see if you can or want to or have time to go to all the places. Once you have an idea of what you can see, check out the prices individually. And remember, a museum pass doesn't get around security check lines and a timed entry is required for the Louvre, Orsay, Ste. Chappelle and many other places. "Skip the line" passes do not mean you walk right in to most places. You can guess that I am not a fan of the pass since the "one use only" rule came into being and made it less of a bargain.
Winter will mean early sunsets, so walking tours (say, with Paris Walks) need to be done earlier on the day. There should be some great Christmas decorations in the city and in stores, etc. Pore over some guidebooks (There are many in the library. They don't have to be the latest issue.) to make a rough plan for your time in Paris. Then you will see if or when you need a private guide.
Oh yes! Notre Dame will be open by then. You might want to attend a mass there (it will be crowded, but the church is huge) on Christmas Day. St. Sulpice church is beautiful and has wonderful music. Of course, you may not want to attend a service that doesn't fit your comfort zone. It will be a religious service first and foremost. And I would try to find a concert somewhere over Christmas. Paris has lots of music venues. I don't know about Christmas Eve/Day though. But after dark you could do a lot worse than an organ or chorale concert.
Best of luck and I hope you have a joteux Noel!
