It will definitely be cold in all of those places (except maybe Venice) during that time of year, but nothing a good warm jacket couldn't take care of
.
That is a tight schedule, though. For me personally, I have found that it takes me at least a day to get adjusted to any city before I can really take everything in, mentally, visually, phonetically, etc...But it is that way, only because I have mentally programmed myself to do that, unless of course, I'm enroute to my main targeted city, then I'll make quick stops along the way as a teaser for a future trip.
Have a great time
!