My response(s) will only address the diving. My question to the two of you is, how long have you been considering scuba? Are you only thinking about it because you are going to Belize or is taking up diving, something that you have long considered? Is it something that you both want to pursue or is one of you just going along with the other?
If you are serious about the diving, then it IMNSHO, you should get certified at home. While you can take all your classroom and pool work at home and then get a referral to finish up in Belize, it is more expensive that way. Taking the certification while on your holiday will take away from enjoyment time, so I'd say that's not a good option for you. Further, assuming you take your home-based training in a lake or more northerly portion of the ocean, I believe that you will enjoy the diving in Belize that much more.
A fish and a bird can fall in love, but where will they build their nest?