We too are building a home on Ambergris Caye. Having made many trips to Belize over the years I try to spend some time on each trip speaking with people that have relocated there to get their impressions. For many it turns out to be a mistake. Often these are people who gave up everything in the States and moved to start a new life. If you plan to spend only part of the year in Belize as we will, you will be in a better position. You can adjust the length of your time there to whatever you like.
Lan's book, by the way, is very helpful in gathering all the published information regarding relocating to Belize into one source. When it comes to getting specific questions answered you will find that it is not so easy. Many of these programs are in their "formative" stages (the QRP in particular), as as a result the answers are not yet available.