This last part is not true and quite the opposite. A unitless noble who was not a priest have it much easier for them to courier gold since priests can be arrested at any time while a unitless noble can only be arrested by chance from "patrols" after a turn and that only happens when there are large amount of enemy troops. While it is true priests can only be arrested by nobles their realm or of enemy realms, that is more than regular nobles and all of things you listed about what can happen to a traveling noble only happens from enemy realms.
A unitless warrior incurs in a chance of being robbed even with very little gold on hands and at his home region. Happened to me more than once.
