Planning a destination wedding is the same job as planning a local one, with two additions: your guests have to travel, and your venue and suppliers are somewhere you are not. Both make the plan longer. What keeps it manageable is taking the decisions in an order where each one unblocks the next.
That order is 12 steps in four stages. The budget and guest count tell you which destinations and venues are realistic. The venue decides which dates are on offer. A fixed date lets you book suppliers and tell guests when to travel, and their replies give you the head count for the final details.
The timings here are a suggested plan built on an 18-month example. The deadlines that bind you are the ones in your venue, supplier and hotel contracts (deposits, room-release dates, final balances) and any set by the authority that registers the marriage.