I think that is just normal yorkie behavior when they are in a new situation with a new dog. When we got our first yorkie (adult) he was fine in the car on the way home (six hours), very calm and docile. When we got him home and introduced him to our new westie it was just as you described!!
Humping and panting like mad!
But by the next day or so he had calmed down quite a bit and was fine. Hope that the home you are thinking of is the right one!
I don't think it would hurt him to be in a crate while you are gone and it sure would save your house!