We were in Rome in January 2yrs ago. The Romans were all dressed up in their fur coats and boots, we were in tee shirts! The nights were much cooler but we found fleeces were sufficient. It was beautiful, sunshine and blue skies every day..
We flew Aer Lingus and got the train from the airport into the Termini. Our hotel was close by and was an ideal spot for touring the city.
The Vatican city is glorious in January. We visited the area late at night when it was quiet. The crib was still up and was beautiful. The crisp clear night air led to the magic of the place.
We went back during the day and the "star" tip we were given was to take along a good size pocket mirror for when you visit the Sinstine Chapel. As you walk along the corridors if you hold the mirror on your palm held in front of you it gives you a fantastic view of the ceilings above without having to strain your neck by constantly looking upwards. It worked an absolute treat.
We bought a guide book before we went and read up on Rome before our visit. We walked and walked and walked for four days and still did not see it all. Guide book was invaluable.
Another tip, if you are on a budget and want a coffee, make sure to have it inside the cafe standing at the bar. It's the cheapest cup you will get. Having it outside raises the price. If budget is not a concern, sit outside and watch the world go by. It's great.
It is a fantastic place to visit. Hope you have a great time.