Welcome to cruise-chat TBtest. Congratulations of picking your first cruise. I did the Valor with the same itenerary this past November. Its a great ship but very port intensive. While in Belize defintely try the cave tubing. I escorted a small group of 25 and set up an excursion for them with an independant tour operator and everyone said that the cave tubing was the highlight of their cruise.
Costa Maya has some great reviews on our sister site Cruisereviews.com, check it out, you will find a host of information on it. You can research all your ports on there.
If you have any specific questions, fire away.