I personally prefer booking directly with the airline unless there is a significant discounted price out there from a reliable Travel Agency. Using Google Flights find a flight schedule & price out here and then click on the link to something like Travelocity. Under the flight details section it will tell you the fees for baggage. If it says unavailable go to the airline's website. As you're flying internationally (though not across an ocean) you will get at least one free bag on most airlines servicing Belize).
AA is a fine airline but it has its own share of bad experiences. Understand about preferring to fly to/from EWR if you're from that general area and the fares all seem to be about the same anyways so no reason to travel to JFK to get to Belize.
You'll be fine & enjoy the trip. Next you could fly your beloved B6 to LIM via FLL.