Ukulelemike

It is difficult to be harmless as doves these days, because culture is continually changing everything about itself on almost a daily basis. What was once racist, like segregation, is now enlightened, so long as people who used to be segregated by force now segregate themselves willingly. Once it would have been considered racists to erase cultural icons of color, like Aunt Jemima or uncle Ben, or the Land O' Lakes Indian maiden, (created by a native American artist), while today, they are erased because people think they images are racist, while disregarding what the actual people behind the icons accomplished, (like the woman behind Aunt Jemima). How do you keep up with a culture that has no boundaries, nothing sure to hold to? So the bottom line is, we hold fast to the word, and preach it without apology, kindly but firmly, and understand that the world has always been, and always will be, offended by the truth of God's word and the gospel.

We know this has to do with God's completed word, and not the coming of Christ, because, 
1: Jesus had already come, and if it referred to Jesus, surely it would say, "He that is perfect is come again"
and
2: Because the scripture, in context, has to do with the supernatural receiving/giving of God's words, through prophecy, tongues and (supernatural) knowledge, or revelation. This is how the Lord gave His word, from Genesis to Revelation-so, in that context, the things we know only in part, (at that time, the word not yet being complete, and only incomplete parts given at any one time), so when that which is perfect, in context, God's completed revelation of his word, was come, there is no longer any need for those partial revelations and prophecies, therefore they would cease.
Context, context, context!

Having been both, let me say, when I first began to preach at the church I am now pastor at, I was, along with some other men from our church, a different church, used to cover on Sundays for the pastor, who was elderly and infirm, and could no longer physically serve fully. I believe that, from the start, they were looking for a replacement, but I was one of about 4 or five that each took a Sunday, and one by one, all the others dropped out and asked me to take over. Shortly thereafter I was asked about becoming the pastor, so I counseled with my pastor on it and he said he would endorse me. (BTW, I had offered myself into full-time service some time before, but had not yet been led anywhere). So I preached on Sunday, they voted, and I was voted in as the pastor, and have been there now 19 years.
So, pulpit supply, as you term it, can become a candidate, depending on the needs of the church and the willingness of the supply to be used of God.
As for how long, that all depends on the church. I have seen churches use fill-ins to preach for years, with no one willing to actually step up to become the pastor, and they just wait for the Lord to send someone, (never thinking maybe He already had them there). But there's really no time limit. As for how long one should be a candidate, I would say that, if they have surrendered to preach, have a good reputation, have preached enough to know they know their Bible and doctrines, hold a vote and get it done.

I will try as well.  Speaking for myself and other IFB's I know and am familiar with what they do, we don't generally follow the Mosaic laws, though we DO consider them as worthy of study, and some aspects are even still good for today. For example: it is still as wrong for a man to wear that which pertaineth to a woman, and vice-verse-why? Because a man is to be man and a woman, a woman. In the NT we see the issue dealt with in hair length-a man is to have short hair, a woman, long hair, each indicative clearly for their sex. At the beginning God made them Male and female, and so we should conduct ourselves always as such, in dress, hair and manners.
Example 2: homosexuality was forbidden in the OT, and repeated in the NT, for much the same reason as the last: created Male and female, the woman from the man, for each other. God's intent, our command.
The issues of clean/unclean: don't sow your fields with differing seed; don't make garments of differing materials; eat these animals, but not those animals: These were all commanded to teach the issue of separation from sin. God wanted His people to behave in a manner differing from the pagan nations, so He taught them to do so by commanding them to do some things different. Even in their clothing there was given a difference, a ribband of blue and a fringe on the borders of their garments, so when they looked upon it they were reminded of God and His laws. So today, though we don't have the same specific things forbidden, through them we learn that God still expects ecclesiastical and moral separation from the lost and their ways.
A for being an antinomian, I'm not sure, I've never nomian'd, so don't know if I'm anti or not. Lol. Seriously, we are to keep the law of Christ and the NT commandments, of which there are many, BUT we are not judged eternally for breaking them, as they were with the Mosaic laws, because today we are saved by grace through faith in Jesus Christ: HE did the work start to finish, and no work we can do will make a difference in our salvation, for or against. However that doesn't mean we should just do as we please-the result of our salvation and our new nature should be to be in obedience to the things of God, and not think out liberty is licentiousness.