Back packing around central and south America any suggestion?

im trying to plan a trip by myself to some central and south American countries. I was wondering if you guys had any tips or comments on where im going and the routes that i will be taking. anything would be very beneficial such as where to and not take the bus . let me first say im 20 year old male my Spanish is alright. i can get by. so im thinking i fly in to cartagena Colombia spend 5 nights there, then catch a bus to caracas( any tips on customs is the bus safe to take there? ) then from caracas i would like to catch a bus to puerto la cruz venezuela spend some nights there. then catch the ferry to margairta island. then from the airport in margarita island i would fly to panama city spend some nights there. then catch a bus to san jose costa rica. then fly home to los angeles. any suggestions would help me out a lot. i plan on being on this trip for 25 days and im bringing about 2000 dollars.