Second the idea of roaming for a while to see where you might want to settle when the roaming gets old. We've been on the road for 7 years now, and there are just too many places we like to pick one or two just yet. We seldom stay one place for more than 2-3 weeks.
For us, it made sense to join 1000 Trails, which has parks in many parts of the country. The upside is that once you pay your dues, the park usage is free. Downside is the upfront cost (always buy a "used" membership and save big bucks) and the tendency to go where the 1000 Trails parks are because they're free, thus missing out on some other great places.
As far as picking a "home base", we opted for a legal residence in South Dakota, so all our paperwork and mail has a place to go. And with about 80 1000 Trails parks around the country, we always have "someplace to go". Kids and grandkids will probably tug on your choice of places to settle once you get to that point.
Since you have a few years, you might consider renting a coach or two for some vacations to get a real life feel for what you like and are comfortable living in.
And one last suggestion - don't wait too long to start your new life. We now wish we'd known then how much fun FT is. We'd have planned a little better and started sooner.
al