Hello Trudy and =welcome to Cruise @ddicts. Please feel free to drop by the community threads and post a hello in the introductions section.
No as to your questions;
1. We are a multi cultural relationship. Please can you advise whether the ship has a variety of races and ages on board? I only ask this question as on a previous ship I was the only person of colour and did not like being constantly stared at!!
I would not concern myself about that one bit. It will be a diverse crowd, although perhaps a little older than the normal Caribbean cruise because of the length.
2. As it is during the celebratory period do you think it would be likely that there will be more formal events, i.e Christmas Day and New Years Eve?
Yes, you can count on special celebrations for Christmas and New Year's
3. We have booked an outside cabin (guarenteed). I actually wanted to book a balcony cabin but was quoted over $5k per person! What are the chances (if any) of being upgraded ?
Probably not from an ocean view to a balcony 
4. Has anybody travelled during the Christmas break? What is the atmosphere like on board?
Have not traveled over Christmas or New Years but I did travel around the 1st of December a few years back and the ship was already nicely decorated for the Holidays.
5. Both my husband and I are into fitness. Do you have to pay for classes such as spinning, combat etc etc?
Not familiar with the two classes you mentioned but there are fitness classes. Celebrity's spas are all very nice and I am sure there will be something for you. The link below has more information.
http://www.celebritycruises.com/whyceleb/singleThumbTxtSub.do;jsessionid=00000L50jsII8z-NfPQCXjXCh_U:12hdebebp?pagename=aquaspa_and_fitness&cS=SIDENAV
You picked a winner with Celebrity. I know you'll =funsign
