GGGGUS, Richard, Bill
These are my thought on this!
There are two thoughts given in these verses by Paul.
The first is that elders who are working for the church may be paid an amount of money to live on by the church to do the work. Vrs 17-18. (see Richard's explanation)
The second thought is that of the accusations against an elder (vrs 19-20), especially one who has been doing the job described in the 17-19.
Refer to the Jewish OT laws of having at least two eye witnesses regarding law breaking/sin/judgment. This is to eliminate a problem of one man's words against another man's words without anyone else witnessing what is being claimed. Without at least two credible witnesses, accusations are not to be heard against the elder. The elder has already been examined in the appointing process and deserves respect for that.
Vrs 20 then sets how the punishment is to be handed out by the church.
These verses have nothing to do with the qualities each man should have to be an elder. The qualities of each man are to be examined before appointment. The actions of each man as an elder are what are to be considered. Has the elder sinned in a way that effects the credibility of his service to and shepherding of the congregation of believers he is serving? Are there at least two witnesses who can personally verify what is being said against the elder? If there are, then the man should be rebuked in front of the church as a whole so that there will be a lesson for all who are witnessing the rebuke. Also, what I don't see mentioned here is removal of the elder from service. It is strong rebuke in front of everyone to act as a warning to everyone but not a removal.
I especially agree with Bill in regard to the idea of qualifications. "Qualifications", which has become a very entrenched word in our fellowship when looking at possible elders, has a meet and pass the test implication and then you don't have to worry about it any more. Qualities are a on-going and very apparent in the actions of the elder. For more on this line of thought, read Lynn Anderson's "They Smell Like Sheep".
I have never been present for an elder rebuking based on 19 & 20. In fact, I don't think I have ever even heard of it being done in the 31 years I have been in the churches of Christ. IMO, it should only be done in extreme cases when all other attempts to correct the man in private have already failed.
It should be a thing of last resort, not first actions.
Regarding vrs 17-18, I do know of paid, full time elders in some churches. However, they tend to also be involved in other duties inside the particular congregation besides being an elder. I have personally served as a deacon under an elder/pulpit minister. I have also served as an elder (unpaid!). The congregation my wife and I attend now has a full time paid elder who is also the full time building maintenance person.
short answers to the questions:
1) see above
2) at least one other witness along with yourself
3) eyewitness, first hand knowledge, etc.
4) if repentance has not already occured--the whole church--see above
5) only after taking the witnesses before the elder in question
7) it applies today
8) can't speak for God.
As I said above, these are my opinions, formed from experience and study. Hope they help.