There is a chapter in The New Creation (1904) (Studies in the Scriptures
Vol. 6) entitled Order and Discipline in the New Creation (Study VI, pp.273 - 347) which can be read in full here. The information below comes from that chapter, particularly the section Discipline in the Ecclesia (pp.289-293).
FFGhost : Was there an "official" procedure that was to be followed?
If one appears to be in error or in sin, his supposed wrong should be pointed out to the erring one only by the one he has injured, or by the member first discovering the wrong. If the reproved one fails to clear himself, and continues in the error or sin, then two or three brethren without previous prejudice should be asked to hear the matter and advise the disputants. (Elders they may or may not be, but their eldership would add no force or authority in the case except as their judgment might be the riper and their influence the more potent.) If this committee decide unanimously with either party, the other should acquiesce and the matter be wholly at an end--correction, or restitution, so far as possible, being promptly made. If either of the original disputants still persists in the wrong course, the one who made the original charge or one of those called in committee or, preferably, all of these together, may then (but not sooner) exercise their privilege of bringing the matter before the Ecclesia, the body, the Church. Thus it is evident that the Elders were in no sense to be judges of the members--hearing and judgment were left to the local body, or Church. The two preliminary steps (above mentioned) having been taken, the facts being certified to the elders, it would be their duty to call a general meeting of the Ecclesia, or consecrated body, as a court--to hear the case in all of its particulars, and in the name and reverence of its Head to render a decision. And the matter should be so clear, and the condemned should have such generous treatment, that the decision would be a unanimous one, or nearly so. Thus the peace and oneness of the body (the Ecclesia) would be preserved. Repentance even up to the moment of the Churchʹs condemnation is possible. Nay, to secure repentance and reform is the very object of every step of these proceedings--to reclaim the transgressor; his punishment not at all the object. Punishment is not ours but Godʹs: ʺVengeance is mine, I will repay, saith the Lord.ʺ (`Rom. 12:19`) Should the wrongdoer repent at any step in this proceeding, it should be a cause of thanksgiving and rejoicing to all who possess the Lordʹs Spirit, and no others are members of his body. `Rom. 8:9` Indeed, even if the transgressor refuse to hear (obey) the decision of the entire Church, no punishment is to be inflicted or even attempted. What then? Merely the Church is to withdraw from him its fellowship and any and all signs or manifestations of brotherhood. Thenceforth the offender is to be treated ʺas a heathen man and a publican.ʺ `Matt. 18:17`
FFGhost : Who made the final determination?
Thus it is evident that the Elders were in no sense to be judges of the members--hearing and judgment were left to the local body, or Church.
FFGhost : What happened if the person was found "guilty"? The New Creation book mentions "withdrawing fellowship", but what did that mean in practice? Everyone, including family? Did "fellowship" mean within the walls of the meeting place, or outside it as well?
There was a distinction between those who commit a sin that incurs death (1 John 5:16) and other sins. In the case of the "sin that incurs death" :
We are not to judge of any by what is in their hearts, for we cannot read their hearts; but if they commit wilful sin unto death it will surely become manifest outwardly--by their lips, if they are doctrinal transgressions, denying the precious blood of atonement; or by their immoralities, if they have turned to walk after the flesh, ʺlike the sow that is washed, to her wallowing in the mire.ʺ It is respecting such as these, referred to in `Heb. 6:4-8; 10:26-31`, that the Apostle warns us to have no dealings whatever--not to eat with them, not to receive them into our houses, and not to bid them Godspeed (`2 John 9-11`); because those who would affiliate with them or bid them Godspeed would be accounted as taking their places as enemies of God, and as partaking of the evil deeds or evil doctrines, as the case might be.
In the case of other sins :
He should not be passed by on the street unnoticed by the brethren, but be treated courteously. The exclusion should be merely from the privileges of the assembly and from any special brotherly associations, etc., peculiar to the faithful. This is implied also in our Lordʹs words, ʺLet him be unto thee as an heathen man and a publican.ʺ Our Lord did not mean that we should do injury to a heathen man or a publican, nor treat either in any manner unkindly; but merely that we should not fellowship such as brethren, nor seek their confidences, nor as New Creatures give them ours. The household of faith is to be cemented and bound together with mutual love and sympathy, and expressions of these in various ways. It is from the lack of these privileges and blessings that the excluded brother is caused to suffer, until he feels that he must reform his ways and return to the family gathering. There is a suggestion in this respect to warmth, to cordiality, to true brotherliness, that should prevail amongst those who are members of the Lordʹs body.
FFGhost : What was the procedure for one found guilty to be "restored"?
It is not within the power of the Church to exclude permanently. The brother who, having offended either a brother member or the whole Church body, returns again and says, ʺI repent of my wrong course, and promise my best endeavors to do right in the future,ʺ or the equivalent of this, is to be forgiven-- fully, freely--as heartily as we hope the Lord will forgive the trespasses of all.