I'm also very interested in flying missions, though my wife has never lived overseas (I grew up all over the world) and she is very apprehensive about it... I don't really feel called to do it right now, but I'm definately keeping my options open. For now I'm just pursuing my ratings to fly commercially in some capacity, don't know if I'll ever do aviation missions.
The 2 largest operaters are MAF and JAARS (part of Wycliffe -> photo to the left is a JAARS Helio). I think they both require a commercial w/500 hrs, 50 hrs tailwheel, 50 hrs high-perf, and an A&P. You'll be working on your own plane in the field. They mostly fly 185's, and 206's with a short-field kit; JAARS have some Helios (they are getting old but probably the most capable bush planes around - 25 kt controllable flight).
Usually spouses are just as involved as pilot/mechanics, and work as dispatchers, schedulers, parts ordering, and everything else. The most important thing for both people is to be doing it for the right reasons - not for the flying (which is probably some of the most exciting out there) but for the chance to spread the Gospel!
