Replying to Backpacking in central america?

Hello newschoolers. My plan for spring break this year is to go backpacking with friends in Central America, preferably somewhere with a beach. I'm not really sure where to start, as far as finding cool places, locations, routes, etc. I've heard Costa Rica is good/safe and a few friends of mine have been to Belize but that's all I've got. If you've done this before and would like to share your wisdom or direct me to a relevant forum I would greatly appreciate it. Note-I'm looking to spend about 3-4 days actually backpacking and then a day or two on each end to potentially explore the more urban areas.