Itineraty suggestion

If I counted right, , you have 5 travel days in 10 days. That's at least 1/2 days per travel day. For 10 days I think you should limit yourself to 3 cities (3 nights per city) so you can enjoy it.

No, I don’t think this itinerary is feasible. Certainly not if you intend to enjoy yourself. You are trying to hit way, way too many cities, which means you don’t actually spend any time IN these places.

Do you have any interest in Rome? You could add several nights there and have plenty to see.
Or is this an Instagram tour, where you take a pic in front of something famous and move on to the next famous spot, just checking off boxes? Or do you want to actually experience any of these places?

With 10 days (including Rome and ending in Nice), I would add one more stop. Barcelona? Prague? Munich? Your choice; just not all three. Preferably someplace with easy train access to Nice.

Its illogical and exhausting. Rome is not my favourite city but many like it - so I'd agree extend time there. Also consider hoping on a train down to Naples and exploring Pompeii and Capri/Sorrento. That alone would take 10 days. Or push it and fly To EITHER Prague OR Barcelona for the last 3 days. However 3 days is not enough for Barcelona

As others commented above— you will not enjoy your trip even if it was possible to actually execute it. Even episodes of TV’s “Amazing Race” don’t move through as much territory as you have listed in the itinerary.
December is cold with rain and/or snow. Plan on spending time indoors as you make your way to Nice from Rome by train. You could visit Orvieto with its underground Etruscan city, Florence for its monuments and Uffizi Gallery, Siena and its Piazza del Campo, and maybe the walled medieval city of Lucca, with its fine restaurants.
Take your time and enjoy!

No, this won't work. Scrap this plan and go back to the drawing board.

IMO your itinerary is in no way feasible. You will spend the vast majority of your trip traveling from one place to the next and will experience almost nothing. Your itinerary is worse than an Instagram trip and beyond exhausting. This does not even take in to account all of the things that could go wrong with the weather during a winter trip. I would suggest you stick to one geographical region. Florence is worthy of several days as is Barcelona. Is your flight home from Nice something that is set in stone, or do you have other options? If you must fly home from Nice, then spend a few days in that region.

Why so much travel, I suggest leaving out the Barcelona portion.

On guided tours, it’s easier to pack in more stops since someone else is handling the logistics for you. This eliminates stress and uncertainty. When you’re traveling on your own, I find it easier to do fewer stops since I know there will be times we have a hard time finding the right train platform or navigating various areas.

Coming off that whirlwind tour of Central Europe by bus, you will most likely be very tired and need a couple of days to decompress and rest. Rome is worthy of a full week's time on its own, but you should consider staying there 5 days if you've never visited there.

Another issue is the weather and cold temperatures in January. It's not the best time of the year to travel to The Alps and to some of the cities farther north that you'd like to see.

Nice is approximately 425 miles from Rome, and it's somewhat off the beaten path of where you'd like to visit. You don't say where your home airport is but flying out of a city like Munich might be a better choice.

Have you considered taking a train to Florence and visit 3 days. Then take a plane or train up to Munich for the remainder of your time. The train takes you thru the Brenner Pass to Innsbruck, and it's just a couple of hours up to Munich from there.

An alternative would be to fly from Rome to Vienna on Ryanair or Wizz Air and go to Salzburg by train on the way over to Munich. We love traveling to Vienna--another great European city.

To add to Dana's post, you are probably underestimating how much time you will have on the ground. For instance
it's about a 2.5 hour flight from Barcelona to Prague. You need to be at the Barcelona airport at least an hour pre-flight to go through security and get to the gate at least 20-30 minutes before flight time. Allow at least 1/2 hour to get to the airport. You'll have to allow more time if you have luggage to check - and you'll have to wait for it at the other end. So you will have to be at your hotel (where your luggage is being held for you) by about 2.30 before going to the airport. If you land at 8, by the time you get off the plane, through the airport, get a taxi and get to a centrally located hotel it's going to be 9 pm or later. When are you going to eat dinner? At 10 pm after to check in? Or at Barcelona airport pre-flight? Or buy something to eat on the plane? Then you're leaving Prague at 6 pm the next day !?! That doesn't give you much time to see the city.

Welcome to the forum, greenandorder-
I'm coming in late here but will agree with all of the previous posters that your proposed itinerary isn't workable if you plan to do any quality sightseeing at all. As it is, the itinerary of your guided tour is distressingly rushed, offering just one full day of sightseeing in two large European cities, and only partial days in all of the other locations. You'll be spending more time in transit and checking in-and-out of hotels than much of anything else. I'd also carefully check the actual locations of the hotels they'll be putting you up in? Some of these "express tours" (lots of places in limited time) choose accommodations far outside historic centers, eliminating lovely evening exploration in those areas.

Granted, it depends on what you want to achieve on this trip, what you're interested in seeing, but we've spent a week in Paris without running out of things to do. While not everyone needs that much time - you may not care to visit all of the museums and monuments that we did - a single full day is still VERY little time for the City of Light.

(Editing to add: it also sounds as if your 12-day tour is occurring over the Christmas/New Year's holiday season. Attraction closures is another concern I have for a a compressed tour itinerary. Many also have regular closures 1 day a week.)

As it sounds as if you've already signed on and it's too late to back out of it, the tour is a done deal so is what it is. I would just caution you not create a similar overloaded itinerary for the 10 days you have on your own. As someone above mentioned, I think as well that you're going to come out of that whirlwind tour exhausted so slowing down is strongly advised. Winter travel, with its short daylight hours and potential for weather-related snags - is also a different animal than travel during warmer months.

One day in Munich is not 'visiting Germany'. A partial day in Prague is not 'seeing' the Czech Republic or even the city itself. Spend some extra time in Rome (fascinating city with a lot to see) and then choose just a couple other locations; some much more feasible itineraries have been suggested by other posters.

Thankyou all for your reply.. I really appreciate it