I notice that a lot of the replies here urge people like yourselves to avoid getting bogged down in preparations. There's a lot of truth to this. Many would-be cruisers (and there are many) are paralyzed by fears and spend years preparing themselves and their boats. By the time they are ready to go, other factors have intervened, forcing them to abandon their plans.
The important thing is to know you and your family's capabilities and those of your boat. Sail within your limits and extend those limits as you build experience. You will find that most passages are on the order of 1 or 2 days. Rare ocean crossings top out at 2 to 3 weeks in a reasonably quick boat. However long a passage, when you arrive in a new port, you will usually find what you need in the way of new and old friends and support services such as provisions, repair facilities, and health care.
The upshot is, don't wait too long to get started. Travel smart and travel safe. There is not need to assume the risks of long ocean passages before you feel ready. Shorter passages will provide plenty of grist in the early going. No exotic skills are required. Do leave before your kids turn 13 if at all possible. If you wait beyond that point, you will explaining to everyone that you are waiting until the kids finish college, which may be too late! If you get them out there before age 13, they will develop an appreciation that will carry them through as they mature during the voyage.
Finally, I suggest you not head out on a "5-year voyage". Start the voyage with the idea that you will continue as long as you are all having fun. Make plans with back doors so that everyone understands that you can exit if things aren't working out. This knowledge does a lot to ease fears that you've gotten into something you can't get out of. In this way, your journey will unfold before you without preoccupation, expectation, and fear...a better recipe for joy and discovery.
Do get it touch if you are able. Also check out our video clip at http://www.3sigma.com/sailing/Final/BigPicture.html