Rob,
It sounds like you are asking 3 independent questions aabout Trail dogs, area Search, and Cadaver search but want one common answer to all three questions,
let me answer you this way, I am a very strong believer in multi-purpose dogs BUT I do not think a first time or a novice handler should be working multi-purpose dogs.
A multi-purpose dog is more complex. I think you should MASTER one project at a time.
Bill T.