I was thinking of you when I saw you were going.
The NH Parque Central is the best hotel to stay at in Havana (hotels can be patchy to say the least) - We stayed 3 days here - its was a perfect base for seeing the city.
I had between 23 and 25 degrees on the computer all week. The south coast is a bit warmer. I was in a 5MM shortie and was fine, but if you feel the cold - you might want a full suit.
Take everything you need, batteries etc, there's nothing to buy out there.
Take plenty of money as well - I was hemorrhaging it all week
Weather was a bit patchy to say the least - 25 -28 degrees most days- but quite windy.
Have a great time