Lizard,
We made the move this year. We did at least two years of research before coming here and this is my advice to you based on our experience.
1. Be mentally prepared. Get to know as much about the country both economically and culturally before even visiting if you are doing so as a reccy to see if you want to live here. It is best to find out what you may or may not like to limit the surprises. Note I say 'limit'. Belize is always surprising.
2. Don't just visit Ambergris Caye. Ambergris Caye is nothing like mainland Belize and you really should have a feel for the whole country before deciding to move. So spend some time traveling during your visit. We spent six weeks in total on AC, Caye Caulker and all across the mainland before making up our mind. Ambergris Caye is much more expensive than most other areas of Belize and Belize is a beautiful country. Not only that but things are different in the various communities across Belize. You may find you prefer somewhere on the mainland.
3. Explore your own mind and be very honest with yourself. Are you able to cope with things not being the same as they are back home? We are constantly surprised by the people we meet who have moved here and now spend their time complaining about things that aren't like back home.
4. If you have explored and you like it, make sure you have a sufficient financial cushion. We decided that we would spend a year here before putting down roots and buying anywhere or starting a business. Lots of people don't do it this way, so I am not saying our way is right, but it has certainly helped. Either way, even if you come down and want to buy a place and set up a business straight away, these things take time and money. Be prepared.
5. The best piece of advice we were given before coming here is 'don't leave your brain at the border'. We almost were swept away with our own enthusiasm and I am so happy we came back down to earth and saw sense before doing anything silly- lots of people do do something silly. Get to know this place and its people before spending serious money here.
Hope this give you some help. As I said, I am not saying what we have done is the best way for everyone, but it has worked for us so far. Just take your time, don't rush, research and then live the dream.