Europe Trip: Narrowed down to London, Paris, Barcelona, Rome, Florence, Prague, Berlin over 18 days. Smart sequence for trip and where should I spend Christmas & New Years Eve?

Some general observations: Your itin looks quite packed and suggest you stay flexible and adapt: Identify types of things you want to take in and type of experiences you will skip, if needed.   European buses, trains and airports work fine thru winter snow and still, the weather can play a major role in the travel experience and introduce unforeseen challenges/opportunities. Because of history, culture and seasonal events, Europeans tend to be more private and internally focused over this season, unlike Spring or Summer.   People tend to get more crowded indoors at smaller shops and cafes. Make sure that you take preventive measures to take care of your health by hydrating, hand-washing, avoiding second hand smoke and taking plenty of rest (even if you have to pass on some of the cities picked).   For Christmas and New Years, many nice places tend to be quite expensive and are booked well in advance. If you decide to stay for cheap, a hostel may be an option. In Florence (and many parts of Italy), you may be able to rent at a local monastery/nunnery, which are generally nice and clean - even if they may not have great insulation to keep you warm. You may need to book in advance.   Depending on your situation, take steps to address your finances so that you can tap into extra funds if there is some unexpected event - airline strike to sickness. Communication (cell phone) costs can also get out of hand if you are still connected to a US carrier and have not made any special arrangements.   If you have friends and relatives -even if not close - in these places, take their contact info with you and don't hesitate to reach them for any assistance  Despite internet and other new tools, local knowledge still rules.   Good luck and happy trails;

Too much!   Some things to consider - on Christmas Day there will be no public transport with the exception of taxis that will be very expensive. This includes getting from the airport to London.   Is there anywhere you must go? And how are you travelling? Airports such as FCO aren't that close to Rome and take about an hour even more to get into the city, and then you will have to deal with potentially poor road conditions and traffic. So in effect you may be spending just one day or less in a town.

I'm sorry to be critical, but aren't you falling into the "if this is Monday, that must be Vienna" American tourist trap?   Why not go to Paris or Barcelona for 18 days and let the magic creep over you? You'll still come home with bags of photos, you'll have had a chance to learn more of the language and you'll be there long enough to have an adventure or three. As well as getting the merest glimpse of the culture.   If you choose Barcelona, be warned, the Catalonians party hard, and they don't need drink to do it. Only tourists try to eat before 21:30.   Personally I think you might find the hardest thing is to see your homeland through other people's eyes. That needs time.