Now, we all know what he should be doing; my question is, what are the ethics involved in this scenario?
First, I'd ask you tease this out a bit further -- as to the distinction of what he
should be doing and what is ethical. I guess I'm looking at ethical as doing what you should be doing!
Allow me to create a very common scenario: a preacher moves to a certain town to plant a church or to take a small church that is unable to provide a salary. He is forced to get a job to make ends meet, not only for himself and his family, but also for some of the needs of the church.
After a while, his sending church or a group of churches take him on for support to the degree that he no longer has to work a secular job. My question is, what is his responsibility, then, to the ministry as far as schedule and time spent doing the work of the ministry? In other words, is he ethically bound to be out knocking on doors, preparing messages, visiting prospects 40 hours a week as if he were still working his secular job?
Taking the scenario as presented, yes, if the preacher is receiving "full-time" support from churches so that he doesn't have to work another job, then it is only ethical that he work "full-time" in the ministry.
This might create some areas that that could be problematic (including just what is "full-time").
A forty-hour work week is a worldly construct (though one that most of us Americans can relate to on one level or another). It seems to me that the biblical workweek is six days shalt thou labour. Expecting the preacher to work 40 hours every week can become very legalistic, especially when judging from a distance. Necessity might require a 50 or 60 hour work week for several weeks in succession, then followed perhaps by only a 30 hour work. Legalists might pay little to no attention to the "extra" hours but key in on why the "short" week. Further, the preacher must be careful to rightfully appreciate and "be worthy of" what he receives, but remember that to his own master he standeth or falleth -- and that his master is the Lord and not the supporting churches.
It is unwise to set up a "bi-vocational" versus "full-time" dispute. It is wrong to approach ministry as something that one always starts out as bi-vocational and then works up to full-time -- or starts out in small churches and works up to big churches. Better to consider "where does the Lord want me for such a time as this" and then be content in whatever state we find ourselves.
If the preacher is energetic and conscientious, and the supporting churches prayerful cheerful givers -- and they all know they must give an account to God -- they should be able to work through problems that arise. If the ethics has to be enforced, the laborer probably doesn't need to be there and probably isn't worthy of support (though I'm not opposed to encouragement, admonition, second chances, etc., before it reaches that point).
When I served as assistant Pastor in Illinois, I drove a public school bus as well.
Bless your heart! May the Lord richly bless you for that!