We had some killer ganja in san pedro. It was so strong that one of our rookie friends couldn't handle it and she had to go lie down in a quiet room so she didn't bug out lol! I loved it, super fun times.
Don't worry about getting busted, just don't be stupid. Everyone will speak english. Like most of the islands you just need to ask the bartender/ferry captain/groundskeeper/pool boy/cab driver and you'lll be set.
Try to also go to caye caulker, its even more laid back. With restaurants like rasta pasta, you can't go wrong.