I've traveled it many times. It is one of my favorite roads. The speed limit is low, the scenery serene and there's plenty of wildlife to view. There are also 2 free campground on this road that are beautiful too. It will have lost its fall colors by December, but still a pretty and peaceful drive.
I did the part in Tennessee many many years ago on a motorcycle. The trees were so dense I couldn't see anything, as I recall. May be more interesting if the leaves are gone and you can see through the trees.
It took me 10 days to do the entire Trace. Ok, I did hole up in one of the campgrounds for 2 nights because it was raining hard and I didn't want to miss any of the sightseeing stops! Yea, I averaged just over 40 miles a day!...
I did it at the end of November so the trees were bare, but the upside is that the number of tourists is WAY down. You have the roads and the stops mostly to yourself.
You'll probably want to make sure you've got propane and a heater.
Before you get started spend some time figuring out how many of the numerous stops you will want to make. If nature walks aren't your thing then plan on leaving them out but even if it's not your thing it's worthwhile getting out and walking at least a little bit of the original trace where it can be accessed from the roadway.