I made the same inquiries into flying down there from the U.S., but was only able to get this info:
1.)You MUST fly in during the daylight hours. Anything flying after dusk better be avian, or you're in deep do-do!
2.)You need clearance from BZE before entering Belizean airspace, and must fly into a previously-agreed upon airstrip(such as BZE), do NOT exit the aircraft until told to do so by the Customs official, who will meet the plane; and
3.)Make sure the flight plan you file with the FAA-FSS is on time, or updated to prevent a search, and at least 15 minutes prior to busting ADIZ on the way back in, or they will bring you down...and the rest(U.S. Customs, etc.), I assume you know.