From my understanding you still have to be in Belize for 3 day prior to getting married. But maybe Pedro has some new info.
Anyway, I used the services at Maya Travel Services (www.mayatravelservices.com
We are having a small ceremony, which started out with just the two of us, but now a few friends are joining us.
You do need two witnesses, which I'm sure the folks at where ever you stay will be happy to be your witness.
Many travel agents will do the license stuff for you. Maya Travel arranged everything for us, license, photographer and minister.
Let me know if you have any other questions....and I'll be sure and report back when I return.