The "Gentlemen's Guide..." as referenced is a good one. Particularly if you want to go south via the Eastern Carib. Alternatively, you could take a more Western route. A couple of options below.
Via
Jamaica. In 2005, we sailed to
Belize via the
Bahamas,
Jamaica, and Bay Islands
Honduras. We jumped off from Acklins (southern Bahamas) to Port Antonio, Jamaica and then to the island of Guanaja in Bay Islands
Honduras (departing from Negril). (In my case I then spent about 7 years in Belize/Guatemala before completing the southern leg of this route just last year.) From Guanaja you can then
work your way "around the corner" to Providencia,
Colombia (actually off the eastern coast of
Nicaragua, but a Colombia possession) and onto to
Panama from there. I made this run last year from Rio Dulce,
Guatemala, to the Bay Islands, Honduras, Providencia, San Andreas, Albuquerque Cays, and ended in Bocas del Toro. Will return to Bocas and
work our way east across Panama in a few months.
Via
Mexico. Many boats come into the Western Carib via the
Florida,
Mexico,
Belize route and then continue on via the route above. Often after spending
hurricane season in Rio Dulce,
Guatemala.