"I think prima scriptura would be a good way to explain my position. The idea of sola scrip is logically indefensible. Especially when the term was coined by a preacher/author/expositer/comentator. I believe the brethren, the spirit, the scriptures and divine circumstance all contribute to leading the saints into truth. I use the ANF (Ante Nicene Fathers) as a commentary to resolve questions and as a testimony where they agree in a catholic way. I.E., all the fathers teach the same about atonement, justification, holiness, baptism, etc. They also singularly voice local custom and specific local and regional issues.
I was headed to bed when I first read your post, so I typed something hurriedly that I'd like to expand on.
Your friend sounds very similar to where I was in the period before I became Orthodox (one reason I can state that he actually is a Protestant. In that time period, I would have rejected the term as well, but with 20/20 hindsight I can see clearly how my thinking grew out of the general Protestant milieu. Not that it's worth arguing with him about). And it's based on that experience, that I would strongly recommend that you focus on an element of doctrine he leaves off his list--'The Church'. What is it and how was it structured.
From Acts 2 on, it is very clear that the Apostles did not just go about convincing people to assent to a list of doctrines on "atonement, justification, holiness, baptism, etc". They went about establishing communities. Baptism was for salvation, certainly, but in the Scripture it also inextricably linked to "being added to the Church (Acts 2:47)". St. Cyprian's treatise is good for this. So is simply doing a search in the Pauline epistles for every time St. Paul talks about 'the body of Christ' or the 'one body'.
Once he has (hopefully) grasped that the 'community of believers' is an integral (and non-optional) part of the early Church he wishes to emulate, then the next question is how is that community structured. "For God is not the author of confusion, but of peace, as in all churches of the saints." (I Cor 14:33) And again Scripture itself is clear that the apostles took care to appoint 'Overseers' (episcopos) and elders (presbyters) to direct the Church once they are no longer physically present. St. Ignatius letters were written within a couple of decades of the death of St. John and to the same communities that had personally known the apostle. And they were written by a man who was on the way to his own martyrdom (i.e., he had nothing to gain from what he said, and said it knowing full well he would soon answer for it). And St. Ignatius is very clear about the integral role of the bishop as the head and central point of the community of believers. Without a bishop, there is no Church. (And as Melodist points out, you can follow this logic consistently down through the rest of the ANF. The role of bishop was never something anyone questioned until the 16th century. And the picture St. Ignatius paints is easily found in the Orthodox Church today.
You can combine this by looking to the Council of Jerusalem as a model of how the Church handled doctrinal questions/and or questions that affected more than a single local church. Notable there is that while all the apostles were gathered there, it is quite clearly St. James who is chairing that meeting, and who proclaims the final decision. St. James was the first bishop of Jerusalem; even secular historians who might avoid the word 'bishop' agree that the historical record is quite clear that after the Apostles left Jeruslem on their evangelistic mission, St. James was head of the church there. And so we see even in Scripture the dignity of the office of bishop, in that even while the Twelve were (mostly) still alive, when they met in council, the local bishop was a full participant in the council with them.
And once you accept that bishops, individually within the local church and as a body for the whole church, are the authorities set in place by the apostles, then it doesn't much matter whether you agree with an individual council or not as time goes on. The bishops were the ones the Apostles appointed to make these decisions--not the individual believer.
It also might be a good idea to spend some time on the Eucharist. The biggest problem here is that there was such total agreement about the Eucharist that there wasn't a lot written about it in the early centuries. Everybody just *knew*. But if you can get past the Protestant error of 'it's just a memorial' to a recognition that something *real* and very sacred is happening with the Lord's Supper, then it becomes kind of inescapable that there must be an 'officiant' through whom that reality is effected. And that leads back to everything St. Ignatius has to say about bishops and how the community around them is united through participation in the Eucharist at which the bishop is the officiant.