Congratulations on booking your first ABD. Unfortunately, I haven’t done the Costa Rica ABD but have done many others. Below are some things to think about and plan while you’re waiting for your trip:
1) Decide if you want to fly in/out the day the ABD starts/ends or if you want to do a pre/post night if they are offered. ABD will have a host hotel for these that you can book through them, but you can also book something, even the same hotel on your own for cheaper most times. Breakfast is included with the pre/post nights that ABD offers.
2) ABD will transport you to the host hotel only whenever you arrive, even if you come in early.
3) Research Costa Rica and see if there are things you want to see that the ABD doesn’t do. These would be good things to do when the ABD has scheduled free time or if you come in early or stay late.
4) Decide if you want to book your own airfare or pay ABD to book it.
5) Review the itinerary to see if there are any meals that ABD doesn’t provide. If there are some, research what restaurants you may want to eat at. The ABD guides will help with this on the trip, but I like to make my reservations ahead of time.
Other than these things, there’s nothing more to do than book your airfare and wait for the trip. Of course there is getting passports, foreign currency, etc. You can always call ABD anytime if you have questions about the trip. Good luck and enjoy.