YES, please make sure you have a non expired passport to travel to Costa Rica.
As soon as you know you’re able to make it to the wedding. The later you book your reservations the more expensive it can be.
Yes, it’s very easy and inexpensive to purchase. Just google “travel insurance for Costa Rica” and many options will pop up. You can also call or email your hotel and ask them what they recommend. If you happen to forget to do this no worries. They have travel insurance you can purchase there at customs.
Yes, but it only rains once a day for 20-30 minutes. Other than that it’s beautiful and sunny. So no worries about bringing a raincoat, unless you want to.