I read all of the quotations and the only reason given (that I could find) for not using musical instruments was because the Roman pagans used musical instruments in their worship. Not one referred to your argument about priests or any similar argument.
However, I don't believe anything outside of the Bible is sacred and is the Word of God. From my readings the Word of God does not prohibit using musical instruments during worship. And there is nothing in the scriptures to indicate that the first century Christians used or did not use musical instruments while singing. You've quoted the scripture instructing us to sing, but I noted that that scripture did not prohibit using musical instruments while singing. The commandment to sing is satisfied whether instruments are used or not.
Well then, I'm afraid you must have skimmed them a little too quickly. The ECF make the distinction between the physical OT and the spiritual NT (it went well beyond Romans here).
CHRYSOSTOM
"David formerly sang songs, ---> also today we sing hymns.
He had a lyre with lifeless strings, ---> the church has a lyre with living strings. Our tongues are the strings of the lyre with a different tone indeed but much more in accordance with piety.
Here there is no need for the cithara, or for stretched strings, or for the plectrum, or for art, or for any instrument; ---> but, if you like, you may yourself become a cithara, mortifying the members of the flesh and making a full harmony of mind and body. For when the flesh no longer lusts against the Spirit, but has submitted to its orders and has been led at length into the best and most admirable path, then will you create a
spiritual melody." (Chrysostom, 347-407, Exposition of Psalms 41, (381-398 A.D.) Source Readings in Music History, ed. O. Strunk, W. W. Norton and Co.: New York, 1950, pg. 70.)
CLEMENT "Leave the pipe to the shepherd, the flute to the men who are in fear of gods and intent on their idol worshipping. Such musical instruments must be excluded from our wingless feasts,
for they arc more suited for beasts and for the class of men that is least capable of reason than for men. The Spirit, to purify the divine liturgy from any such unrestrained revelry chants:
'Praise Him with sound of trumpet," ---> for, in fact, at the sound of the trumpet the dead will rise again;
praise Him with harp,' ---> for the tongue is a harp of the Lord; '
and with the lute. praise Him.' ----> understanding the mouth as a lute moved by the Spirit as the lute is by the plectrum; '
praise Him with timbal and choir,' ---> that is, the Church awaiting the resurrection of the body in the flesh which is its echo; '
praise Him with strings and organ,' ---> calling our bodies an organ and its sinews strings, for front them the body derives its Coordinated movement, and when touched by the Spirit, gives forth human sounds; '
praise Him on high-sounding cymbals,' ----> which mean the tongue of the mouth which with the movement of the lips, produces words.
Then to all mankind He calls out, 'Let every spirit praise the Lord,' because He rules over every spirit He has made.
In reality, man is an instrument arc for peace, --->
but these other things, if anyone concerns himself overmuch with them, become instruments of conflict, for inflame the passions.
The Etruscans, for example, use the trumpet for war; the Arcadians, the horn; the Sicels, the flute; the Cretans, the lyre; the Lacedemonians, the pipe; the Thracians, the bugle; the Egyptians, the drum; and the Arabs, the cymbal. ---> But as for us, we make use of one instrument alone: only the Word of peace by whom we a homage to God, no longer with ancient harp or trumpet or drum or flute which those trained for war employ." (Clement of Alexandria, 190AD The instructor, Fathers of the church, p. 130)
(Note the quote and exposition on Ps 150, an often quoted Psalm here, above)
The ECF compared and contrasted earthly (OT) instruments with spiritual (NT) ones. The OT is but a shadow of the more perfect thing to come.
WE are the instrument with which we praise God more perfectly. This is what Paul is trying to say in Eph. "sing and make medody" (with what??) "in your hearts". It is the "heart strings" we are to play through our voices. Anything else is simply less, in the way, and can "inflame the passions" (can actually have a negative effect, and don't tell me you have not seen music turn into performance art, and the main event itself, for I know you have. We all have.)
Now as I have stated here many times before, I do not consider the ECF anywhere on par with Scriptural authority. If an ECF disagrees with Scripture, he must be rejected. If you cannot handle them properly, I would prefer that you ignore them altogether. However, I am guessing you are mature enough to weigh them properly, so I leave them to you. If nothing else, what they do is provide an insight as to how the earliest Christians viewed the Scriptures, and this can be quite useful as secondary evidence in matters where there is disagreement. If we are truly going to call ourselves a "Restoration Movement" and go back to the 1st century practices, it might be useful to find out what those were. From the biblical and historical evidence, if you say it cannot be determined if the earliest Christians used instruments or not, you are simply seeing only what you want to see and not being honest with yourself. The evidence is overwhelmingly clear. The only question left is, "Why not?", and they even answer that question in their writings.
Regarding infant baptism, Peter told the crowd to repent of their sins and be baptized for the forgiveness of their sins. I personally don't believe an infant can repent of its sins and I don't believe an infant has any sins.
The danger in "baptizing" infants (other than getting wet) is they will be told they have been baptized and as adults may never be baptized as Peter instructed...for the forgiveness of their sins. They will meet Christ unbaptized. And we know how they will be received by Christ because of what Christ Jesus said in Matthew 7:21-23:
By the way, I have yet to hear of an infant being property baptized, i.e. immersed.
On this we do agree.....
I believe the Orthodox Church may immerse infants, but to be sure, ask an Orthodox.