After you arrive in Belize City I'd take a bus out to Cayo District, San Ignacio for 5 days. Then either rent a car(nice drive through Hummingbird Highway) or bus it to Placencia for another 5 days. After that you can fly/bus to Belize City and go out to the Cayes from there. Spend 4-7 days in CC and your 14 days in San Pedro.