Don't even go there unless you come from a family with means and have friends with plenty of disposable income and very flexible schedules.
In this economy, I'd just skip inviting others, and go get married on the cruise or carribean get away without them. You're asking to have your dreams dashed and not having a nice wedding a second time by putting it on others to find the money AND time off from work and life to join you at a destination wedding.
I totally resented it when friends and relatives invited me to high expense weddings like this because it creates unnecessary guilt! It doesn't matter if you say they aren't obliged to go. They WILL feel obliged, and most will make the sacrifice and go, even if it means they'll be broke for the next two years. The mere fact that you asked. puts undue pressure on them to find the money and come, lest they feel like they're disappointing you or out of fear that you might think they don't love you or care.
It's an imposition to do this, and in my opinion bad taste. You've had years to plan and save. Your relatives and friends didn't. If they have kids, they will now have to choose between coughing up funds to bring them along (if you'll allow children at your wedding) or will need to find a sitter willing to watch them for an entire week or weekend.
Then there's the expense of gifts, attire, the cost of the flight ( if it isn't included), possibly hotel costs, and needing just general spending money to be able to have a somewhat decent time at the resort or on the cruise after the wedding festivities are over. That adds up fast.
Don't do it, I say! If they don't have the money, these "guests" will be the worst thing that can happen to your wedding. You'll either have to deal with incessant complaints, moodiness and outright confrontation or anger directed at you, and you'll be stuck with these people after the ceremony. If they're not happy, you certainly won't be happy. It will add up to a very bad vacation and you'll be wishing you'd saved the money for THIS wedding and stayed home.
Just remember, for the guests (whether it's parents, cousins, your closest friends) this isn't their idea...or their suggested gift to you. You are imposing on them, and while they'd never tell you to your face you're a jerk for doing this, they'll probably harbor resentment and think it all through the whole trip, and long after if they have to put it on credit cards or sacrifice something for their own family to appease you and your fantasy destination wedding.
If you really want a traditional wedding with witnesses and guests, plan it that way....in a LOCAL church...at a LOCAL hotel, resort or park and then go on your dream destination vacation AFTERWARDS and without friends and family. Don't put people on the spot trying to accommodate your personal needs or interests. It isn't fair.
Sorry to be so harsh or wet blanket, but hopefully you do realise, that if a total stranger could say this based on their own experiences of being invited to weddings like this (which by the way, for me were absolutely miserable and with one friend, we don't speak anymore), you can bet your own family very likely would feel the same. So if you don't want unnecessary drama or tension surrounding your long awaited dream wedding, don't go there! JMO.