You aren't hiring a calligrapher to carefully handwrite your invites (unless you are, then OK GIRL, GOOD FOR YOU), you're doing it yourself. So order at least 15-20 extra envelopes for when you end up spelling your grandma's name wrong or writing the wrong state code.
Congratulations on your engagement and your decision to host a destination wedding for all your friends and family someplace fabulous, tropical, and remote. You have a responsibility to make your guests' trip -- both planning and execution -- as smooth as possible for each and every one of them.