Give yourself plenty of time. Set the "seed" of an idea; imagine it is possible; and commit to the concept.
For us it started long ago (or perhaps has always been with us) the urne to travel. The "seed" for "Philomena SOL Tour" was set in 1999, on a hike up Mount Pisca. Dave and I left our then 4 month old daughter and 5 year old son in the capable hands of "the village" of aunts, uncles and Grandma. It was during that hike that we committed to the concept of taking "a year off" to travel as a family, and decided that ideal timing would be when our youngest was old enough to remember and our oldest was young enough for it to still be acceptable to be with one's parents. That narrowed the travel window to 2008-2009: and, here we are today, setting out with kids are 9 and 13 years old respectively.
There were several million details to deal with to get to the point of going: homeschool plans, renting our house, purchasing and services Philomena (1984 VW Westfalia camper van), collecting gear, maps, stories and books; down loading books on tape and cd; route planning; contacts; and on and on... Lists help; chip away; have faith; here we are: night three on the road and loving every minute thus far. A highlight today "Dismal Pool" Crawford Notch, NH.